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The car is a vtec, 4 cylinder, automatic trans in a four door EX body. This car has 180k on the clock and has had a tuneup, IACV and throttle body cleaned. This problem started about three months ago prior to this work. When you start the car it idles smoothly at around 1,200 rpm. After about three minutes the idle slowly falls to around a 900 and starts getting rough. The idle gets rougher and rougher and suddenly jumps up to 1,500 rpm for a split second and back down smooth again. The car may then be driven normally and will accelerate perfectly and strongly if need be. This little process takes about four minutes and the engine is nowhere near actually hot at this point.
If you try and drive the car before this ritual it will bog down, choke and feel fuel starved. You keep pressing the pedal harder but the rpms slowly drop. The car feels like a failing fuel pump. Jumping forward, surging, bogging down. After a mile of struggle and she runs like new! Any thoughts?
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Before you try anything, you should get the codes pulled. Most autoparts stores will do a scan for free.
I’m sorry I didn’t mention it. There is no check engine light and a scan at the parts store this weekend showed no pending codes either. It also has had a new fuel pump. I wanted to test the fuel pressure but the loaner test kit I had would not fit on the car’s test port. This thing is really frustrating. Now I know why drivability diagnostic techs get paid better.
Ok. This is gonna sound weird but I am about to compare your car to a go-cart. Im not trying to be funny. I had a go-cart that did the exact same thing. When you would try to go before it warmed up a little it would almost stall. Now by this point your probably lauging but seriously. You mentioned it has 180,000 miles on it. Have you changed the fuel filter? The float in the gocart was sticking so maybe you have a fuel delivery restriction… Im no mechanic i just know only a little bit.
does the idle ever drop to 700-750? 900 is
to high for a base idle. try tapping the IAC
with the handle of a screw driver to see if the
idle changes.if it does change the IAC.also look
for vacuum leaks.The car idles when warm around 500 rpm. The fuel filter is attached to the base of the fuel pump and is new. The 1997 has an extra one in the engine compartment. Mine does not. The idle air control valve is new but I have not hit it with a screwdriver. May try that out. I used carb cleaner to check for vacuum leaks once before. No luck on that one.
I don’t have a scan tool but my brother in law is bringing his this Christmas when they visit. Very handy.
Don’t forget to also check for vacuum leaks and under no circumstances should the screw on the throttle body be adjusted to correct the idle. This can actually mask the real problem and make diagnosis difficult. Also once you’ve fixed the problem you’ll need to go back and reset the base idle. I mention this because I see this a lot. You might have already fixed the problem when you installed the new IAC but if the idle screw was adjusted then the computer may not be able to put the idle into spec and therefore you have an idle issue.
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