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Hi everyone!
So I have an up until now faithful 1994 Accord EX 4-door Automatic with VTEC engine. All of a sudden about a month ago it started surging intermittently and it’s gotten worse. I thought it was an idle issue at first (CEL code 14 persists to this day) but now it’s doing it all the time even when the throttle is open. The RPM goes up and down, RRR – RARR — RRR — RARR — you get the idea. It’s bad enough that the engine moves back and forth like its nodding it’s head.
I’ve tried everything I found online as a remedy (thanks to Eric for the videos). Here is what I’ve done so far, some of which seemed to fix it but after a day or two it disappointed:
New spark plugs NGK iridium
New spark plug wires NGK
Royal Purple injector cleaner added to premium gas
Cleaned out original Idle Air Control Valve
Adjusted Fast Idle Thermo Valve
New distributor cap and rotor (did this twice, Duralast then YEC)
New air filter
New pcv valve (oem)
New antifreeze/coolant (oem) — bled system too, after every part change involving coolant lines
Replaced Idle Air Control Valve with New part
Replaced Fast Idle Thermo Valve with New part
New synthetic oil and filter
Disassembled throttle body and cleaned it out very very well including both sides and edges of butterfly and IACV passage, replaced TB gasket
New Throttle Position Sensor calibrated to .5-4.5 (original one tested fine too)
Tried removing vac line (plugged it) and wiring connector from EGR, no change in symptoms
Tried removing wiring connector from IACV, no change in symptoms at speeds above idle
Tried adjusting idle speed screw (paid a mechanic for diagnostic and that’s all he came up with unfortunately) which seemed like a fix but wasn’t.
Tried placing hand in front of open throttle body and engine stalled completely and quickly after hand was sucked up to the opening, my understanding is that pretty much eliminates a vacuum leak as the culprit?
Little to no suction on lower port in TB (FITV)
Lots of suction on upper port in TB (IACV)
Any troubleshooting ideas I can try?
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Forgot to mention I did try spraying carb cleaner around on all vacuum interfaces I could see with the engine running. The back of the manifold gasket was out of reach. Not 100% sure but don’t think it’s a vac leak. As mentioned anything else I can try (test procedures) would be appreciated.
Did you mean the bottom side of the intake manifold gasket was outta reach? Those gaskets tend to leak a lot because of the valve cover gaskets leaking oil on them. After a while the oil starts eating away at the gasket and deteriorates it. Try spraying all the way around the gasket, but mostly on top. It honestly sounds like a vacuum leak since you’ve tried everything else. I was going to mention the idle screw adjustment but you mentioned that. Did you put the paper clip in the service connector and disconnect the IAC while you adjusted the idle screw? You also have to make sure it’s at operating temp (when the fans kick on).
http://ww2.justanswer.com/uploads/thebesthonda/2010-03-09_163135_dtc_14.pdf
This may also help
I mean the back side of this gasket circled in red, it’s against the firewall so hard to spray. It’s just a guess, you know, Murphy’s law that it would be the one thing you can’t reach.
Another thing I could try is taking off the EGR valve and cleaning what I can there. I’m not sure that would make any difference because I did try it disconnected and symptoms persisted.
I think I’ve pretty much tested everything on that flowchart you provided (thank you though) so it seems to indicate trying a different ECM. Ouch. Kind of hard for a non-professional to just happen to have a spare ECM on hand. 🙂 Any other way to see if the ECM is at fault rather than swapping it?
I didn’t use the service connector (I assume you mean the same one where I get the CEL code) and disconnect the IACV while adjusting the idle screw, I’ll have to try that.
Sadly I came down with a bad cold but I think I’m getting over it so I can try to get this car back on the road soon. I’ll report back!
Hondaguy, I tried setting the idle speed using the method you suggested, my impression is it didn’t make any difference. The problem is so intermittent it’s a little frustrating because the car will behave fine for a while and I think I’ve fixed it and then a day later it’s undrivable.
Just FYI Hondaguy here are some test results from the IACV backprobe I did today:
engine cold:
both idle and open throttle surging/rough
13.4v constant when acting up
7-8v when behaving for a momentengine warm:
4.4v constant regardless of throttle position (behaving now)
idle smooth most of the time
surging problem arises intermittently while driving or idlingdisconnect IACV: virtually no change, idle drops maybe 100 rpm
I also noticed when the car is started (engine warm) that it bounces up and down between 1500-1600 RPM (sounds like the surging issue) then up to 2500 RPM then down to normal idle speed. When the car was healthy it didn’t do that.
Now, if this were a vacuum leak, wouldn’t the car have the issue all of the time?
[quote=”ben_tech” post=156471]Hondaguy, I tried setting the idle speed using the method you suggested, my impression is it didn’t make any difference. The problem is so intermittent it’s a little frustrating because the car will behave fine for a while and I think I’ve fixed it and then a day later it’s undrivable.
Just FYI Hondaguy here are some test results from the IACV backprobe I did today:
engine cold:
both idle and open throttle surging/rough
13.4v constant when acting up
7-8v when behaving for a momentengine warm:
4.4v constant regardless of throttle position (behaving now)
idle smooth most of the time
surging problem arises intermittently while driving or idlingdisconnect IACV: virtually no change, idle drops maybe 100 rpm
I also noticed when the car is started (engine warm) that it bounces up and down between 1500-1600 RPM (sounds like the surging issue) then up to 2500 RPM then down to normal idle speed. When the car was healthy it didn’t do that.
Now, if this were a vacuum leak, wouldn’t the car have the issue all of the time?[/quote]
Did you try resetting the computer after doing all of these changes to the idle mixtures?
Also hows your thermostat? During the winter here in Texas my OE thermostat failed open and when I would get off of a highway the engine RPMs at idle would surge, new thermostat solved that for me.[quote=”DaCoder” post=156476]Did you try resetting the computer after doing all of these changes to the idle mixtures?
Also hows your thermostat? During the winter here in Texas my OE thermostat failed open and when I would get off of a highway the engine RPMs at idle would surge, new thermostat solved that for me.[/quote]Yessir I have reset several times with the two fuses but not today. Don’t think I did anything magic today that would make a difference.
How to test thermostat? hate to keep replacing parts without testing first. 🙂
[quote=”ben_tech” post=156478][quote=”DaCoder” post=156476]Did you try resetting the computer after doing all of these changes to the idle mixtures?
Also hows your thermostat? During the winter here in Texas my OE thermostat failed open and when I would get off of a highway the engine RPMs at idle would surge, new thermostat solved that for me.[/quote]Yessir I have reset several times with the two fuses but not today. Don’t think I did anything magic today that would make a difference.
How to test thermostat? hate to keep replacing parts without testing first. :)[/quote]
Well the only reason i brought that up is if you notice on a really cold day, your car never gets up to temperature. Mine would take AGES to get to working temps and then on the highway would drop down to almost on the C mark, until I came to a stop, then the idle would go crazy.
If you notice it takes a while to heat up, or doesnt stay constant after getting there, it might be the thermostat.[quote=”DaCoder” post=156479]Well the only reason i brought that up is if you notice on a really cold day, your car never gets up to temperature. Mine would take AGES to get to working temps and then on the highway would drop down to almost on the C mark, until I came to a stop, then the idle would go crazy.
If you notice it takes a while to heat up, or doesnt stay constant after getting there, it might be the thermostat.[/quote]Right I understand why you brought it up however it’s definitely not the case with this car unfortunately as that looks like an easy fix. After a little reading I see what the symptoms of a bad thermostat are. In my case the engine temp needle is stable and right where it should be on the mark between hot and cold and gets there within 5 minutes on a cold day and the heater works fine… and there is no steam…. so the thermostat is *probably* OK. Thanks for the idea though good to mention it as I’m grasping for possibilities.
[quote=”ben_tech” post=156480][quote=”DaCoder” post=156479]Well the only reason i brought that up is if you notice on a really cold day, your car never gets up to temperature. Mine would take AGES to get to working temps and then on the highway would drop down to almost on the C mark, until I came to a stop, then the idle would go crazy.
If you notice it takes a while to heat up, or doesnt stay constant after getting there, it might be the thermostat.[/quote]Right I understand why you brought it up however it’s definitely not the case with this car unfortunately as that looks like an easy fix. After a little reading I see what the symptoms of a bad thermostat are. In my case the engine temp needle is stable and right where it should be on the mark between hot and cold and gets there within 5 minutes on a cold day and the heater works fine… and there is no steam…. so the thermostat is *probably* OK. Thanks for the idea though good to mention it as I’m grasping for possibilities.[/quote]
I have been reading up on this, and some people said their ECU was the issue, but the majority I have read about say that the coolant temp sensor was working intermittently, have you checked that? You can take an ohm meter to it after the car has warmed up.
EDIT: On our cars there are multiple coolant sensory: one on the upper rad hose outlet, one on the thermostat housing, and two under the distributor. Upper rad hose is the fan control switch, thermostat housing is ALSO a fan control switch (one is for both fans and the other is for one fan), under the distributor is two sensors, one is for the readout on the dash, the other is for the ECU. The latter is what you would need to test.
Spent all afternoon on this today.
Tested IACV harness yellow/black wire to ground got battery voltage constant – PASS
Looked at engine grounds G1 G2 and G101, all look tight and no loose wire strands or any obvious corrosion
Tested MAP sensor. Results:
5v – pass
gnd – pass
signal – 2.91v decrease gradually to 2.79v with suction by mouth then back to 2.91 – passCleaned EGR passages in manifold – one passage was blocked completely with carbon – big job
Cleaned EGR valve
End of the day, no change, she’s still bucking like a mule (CEL code 14 as always).
Sprayed carb cleaner all around Manifold B gasket as best I could with poor access to back of it. Felt all around it with bare hand also, hoping to feel a breeze. Didn’t notice anything.
Worth repeating (or in case I didn’t mention it yet) that the engine bucking still happens with the IACV harness disconnected. Idle is lower as expected and smooth but opening throttle brings back the bucking. With IACV connected the bucking happens at idle when the engine is cold but when it warms up it seems to happen more with the throttle open, but sometimes at idle too (intermittent). Today it was really bad (weather: cold, rainy).
Will have to look into the coolant sensors for my next work session.
Any and all testing/troubleshooting tips for my engine bucking problem would be most welcome.
[quote=”DaCoder” post=156482]I have been reading up on this, and some people said their ECU was the issue, but the majority I have read about say that the coolant temp sensor was working intermittently, have you checked that? You can take an ohm meter to it after the car has warmed up.
EDIT: On our cars there are multiple coolant sensory: one on the upper rad hose outlet, one on the thermostat housing, and two under the distributor. Upper rad hose is the fan control switch, thermostat housing is ALSO a fan control switch (one is for both fans and the other is for one fan), under the distributor is two sensors, one is for the readout on the dash, the other is for the ECU. The latter is what you would need to test.[/quote]
DaCoder, I’ve been looking around at all of the sensors in there and I’m not quite sure which one.
I took a picture under my distributor cap and circled the sensor I think is the coolant sensor specific to the ECU:
[IMG]http://i204.photobucket.com/albums/bb130/7h645764n57/coolant-sensor_zpsbveklew1.jpg[/IMG]
Is that the right one?Can this be tested in place? I’d test the harness voltage and ground with the key in the accessory position and I assume ohms on the sensor while the car is off. Can I backprobe the electrical plug while the car is running and see the sensor vary the ohms reading as the coolant heats or does it have to be measured without the electrical connection attached? I saw the hot water technique but you have to remove the sensor to do that and I’m a little tired of draining and bleeding coolant at this point.
Also today I did place a piece of cardboard in between my Fast Idle Thermo Valve and the throttle body as I read that’s a way to eliminate that part as a suspect. No change.
I’m also looking at doing some continuity tests between the Idle Air Control Valve wiring connector and wherever it connects to the ECU/ECM. I have the Honda shop manual but quite frankly I can’t find anything in that thing. So if anyone can point me to where the other end of those wires are that would be great.
[quote=”ben_tech” post=156664][quote=”DaCoder” post=156482]I have been reading up on this, and some people said their ECU was the issue, but the majority I have read about say that the coolant temp sensor was working intermittently, have you checked that? You can take an ohm meter to it after the car has warmed up.
EDIT: On our cars there are multiple coolant sensory: one on the upper rad hose outlet, one on the thermostat housing, and two under the distributor. Upper rad hose is the fan control switch, thermostat housing is ALSO a fan control switch (one is for both fans and the other is for one fan), under the distributor is two sensors, one is for the readout on the dash, the other is for the ECU. The latter is what you would need to test.[/quote]
DaCoder, I’ve been looking around at all of the sensors in there and I’m not quite sure which one.
I took a picture under my distributor cap and circled the sensor I think is the coolant sensor specific to the ECU:
[IMG]http://i204.photobucket.com/albums/bb130/7h645764n57/coolant-sensor_zpsbveklew1.jpg[/IMG]
Is that the right one?Can this be tested in place? I’d test the harness voltage and ground with the key in the accessory position and I assume ohms on the sensor while the car is off. Can I backprobe the electrical plug while the car is running and see the sensor vary the ohms reading as the coolant heats or does it have to be measured without the electrical connection attached? I saw the hot water technique but you have to remove the sensor to do that and I’m a little tired of draining and bleeding coolant at this point.
Also today I did place a piece of cardboard in between my Fast Idle Thermo Valve and the throttle body as I read that’s a way to eliminate that part as a suspect. No change.
I’m also looking at doing some continuity tests between the Idle Air Control Valve wiring connector and wherever it connects to the ECU/ECM. I have the Honda shop manual but quite frankly I can’t find anything in that thing. So if anyone can point me to where the other end of those wires are that would be great.[/quote]
So I have in my possession a Full Service Manual, let me go through and find these two answers for you. I will edit this post with my findings.
EDIT_1: Found it, that is indeed the sensor in question, the one next to it goes to your dash temp gauge. Still looking for the IACV wiring diagram. Also will find you the test procedures for the coolant temp sensor.
EDIT_2: Found this in the FSM, good way to see if an ECM replacement is required or not.
EDIT_3: Found out that almost every power sucking device sends inputs to the ECM when they turn on / off, could be that aswell. This seems to me now to be the most likely issue. This is because I found out that a code 6 would indicate the ECT (the part we were looking to test) is having issues. If you wish to test it however, run engine until hot, take off connector, measure resistance between the poles, if its within 200-400 ohms its good.
EDIT_4: Finally found the connector diagram for the IACV system:
[quote=”DaCoder” post=156665]EDIT_1: Found it, that is indeed the sensor in question, the one next to it goes to your dash temp gauge. Still looking for the IACV wiring diagram. Also will find you the test procedures for the coolant temp sensor.
EDIT_2: Found this in the FSM, good way to see if an ECM replacement is required or not.
EDIT_3: Found out that almost every power sucking device sends inputs to the ECM when they turn on / off, could be that aswell. This seems to me now to be the most likely issue. This is because I found out that a code 6 would indicate the ECT (the part we were looking to test) is having issues. If you wish to test it however, run engine until hot, take off connector, measure resistance between the poles, if its within 200-400 ohms its good.
EDIT_4: Finally found the connector diagram for the IACV system:
[/quote]Thanks! I’ll probably go ahead and test the coolant temp sensor since it sounds easy to do.
What “seems to me now to be the most likely issue”..,.. faulty ECM?
On the IACV test from the service manual it says to use a honda test harness which I don’t have. I’m wondering if I can somehow find the correct wires (A9 and A23) on the harness right at the ECM and backprobe with needles to accomplish the same thing. Maybe it will be more apparent when I get in there and look at it.
[quote=”ben_tech” post=156668][quote=”DaCoder” post=156665]EDIT_1: Found it, that is indeed the sensor in question, the one next to it goes to your dash temp gauge. Still looking for the IACV wiring diagram. Also will find you the test procedures for the coolant temp sensor.
EDIT_2: Found this in the FSM, good way to see if an ECM replacement is required or not.
EDIT_3: Found out that almost every power sucking device sends inputs to the ECM when they turn on / off, could be that aswell. This seems to me now to be the most likely issue. This is because I found out that a code 6 would indicate the ECT (the part we were looking to test) is having issues. If you wish to test it however, run engine until hot, take off connector, measure resistance between the poles, if its within 200-400 ohms its good.
EDIT_4: Finally found the connector diagram for the IACV system:
[/quote]Thanks! I’ll probably go ahead and test the coolant temp sensor since it sounds easy to do.
What “seems to me now to be the most likely issue”..,.. faulty ECM?
On the IACV test from the service manual it says to use a honda test harness which I don’t have. I’m wondering if I can somehow find the correct wires (A9 and A23) on the harness right at the ECM and backprobe with needles to accomplish the same thing. Maybe it will be more apparent when I get in there and look at it.[/quote]
Probably, if the surges still happen at full throttle.
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