low idle speed randomly when hot

[Matt]

I have a 2001 Toyota Corolla AE112R AUTO with a 7A-FE engine (if this helps), a while back i had a blocked IAC valve which made my car idle low when cold (~500-600 rpm) and idle high when hot (1200-1300rpm) – i removed the IAC and cleaned it out and fixed that issue (back to cold = ~1100-200rpm, hot = 900-1000rpm, IAC was jammed ~30% open).

Now i have noticed when the car is hot (temp gauge right in the middle – normal operating temprature) the car will sometimes drop to ~500-600rpm when im stopped in traffic/at lights etc – i watch the revs drop in small ammounts as if the computer is adjusting the idle a bit at a time via the IAC.

If i turn on the aircon it jumps right back up to 900-1000rpm aok and when i turn it off it will usually drop back to ~900rpm for a while then start to drop. It usually takes ~10 seconds for it to drop to its lowest point.

The car never stalls or struggles to start, if im on a hill and the car rolls back it doesnt cut or stall either, it runs smooth and doesnt run rough at all even during the low revs.

When the revs are low on a flat surface my car will not move so i have to accelerate and it feels as if i have to sink my foot further down on the accelerate/move the car.

I have tried resetting the ECU/computer via unplugging the battery for ~half an hour – my car felt a bit more powerful and did change a little but still has the same issue.

I have also does the usuals – check filters, oil, injector cleaner, cleaned the airflow sensor with the correct spray etc – all good.

Any suggestions? Thank you in advance!

Topic

[EricTheCarGuy]

I don’t often have any luck cleaning IAC valves which is why I choose to replace them instead. You might try replacing the IAC and then rechecking for the problem.

[Matt]

I kind of overlooked the IAC because it seems to respond to everything aok compared to before i cleaned it like i had this thing out in my hand, before cleaning it wouldn’t move as to now where it moves freely, and cold/hot the car seems to behave correctly.

I also tested it with a 9v battery – it responds (open/close) 100% – its a simple 3 wire magnetic driven IAC (cars are not really my thing but electronics are).

I dont want to sound like im ignoring your answer im grateful you have taken the time to read my post 🙂

This is ~10 minutes driving, stop in traffic then as im watching the revs it will in ~100rpm lots every 1 second (down, wait, down, wait etc) go down all the way to ~500rpm. Sometimes it will just go down to 500rpm when i pull up it will go direct to 500rpm so not just sitting around stopped, if the aircon is on it wont show up?

I really feel as if the car computer is trying to make the engine idle as low as possible (when hot) without vibration/stall – or almost as if someone re-programmed the computer so it idles lower when hot – is that even possible? (aka instead of fixing IAC just program in low hot idle to counteract it not working??)

Is there any other sensors (O2, temp, maf etc) that could throw this off and make the car when hot try to lower the revs?

Im getting a basic code scanner for the car incase it can find something so if it does (when i get it) ill post back with the details.

Again thankyou for your response, if you say IAC i will try replacing it when i get a chance.

[dreamer2355]

Doe you have a CEL?

And i would recommend a bi-directional scan tool or at least one with PID data.

How many miles are on the vehicle?

[Matt]

no warnings at all

im going to pick up a basic scanning tool next week

the car has done 175,000 KM

im also try getting a video of the revs drop too because it does it in steps

[Matt]

http://wiki.answers.com/Q/How_do_you_adjust_idle_for_Toyota_paseo

this sounds like what i have been talking about – “hot” idle speed set too low, and matches what i thought where the last owner or mechanic set it lower to counteract the blocked IAC problem (low cold idle, high hot idle) by setting the hot idle speed lower.

ill post back and let you know if this works

[EricTheCarGuy]

If it was something like a vacuum leak or issue like that I would think it would behave the same all the time, what happens with yours is an intermittent problem with a high or low idle which would indicate an electronic issue. Based on the fact that you don’t have a check engine light on I would say that the IAC is the most likely cause. I would suggest replacing it and then rechecking for the symptom.

[Matt]

problem solved

both my problems were related (http://www.ericthecarguy.com/component/kunena/8-Service-and-Repair-Questions-Answered-Here/34218-car-doesnt-like-50kmh)

solution (http://wiki.answers.com/Q/How_do_you_adjust_idle_for_Toyota_paseo)

Idle base line set too low, once the car warms up the IAC closes up which drops the revs to the base speed which was set far too low, when i got the car the IAC was jammed half open, (hot idle too high, cold idle too low) the old owner or last mechanic would have just set the idle lower (fix high idle when hot) rather then take out and clean the IAC, after i clean the IAC it resulted in the low idle set by them.

Now the car idles (cold) 1100rpm, and warm ~850-900rpm, aircon on = ~900rpm still.

Thankyou for all your help and suggestions.

[college man]

Thanks for the update and the fix.

[dreamer2355]

Thanks for posting the fix and providing those links!

[EricTheCarGuy]

Awesome. Thanks for the update, the fix, and for using the ETCG forum.

[Matt]

Update

I checked out all the vacuum lines, PCV and Charcoal Canister – the PCV wasn’t sealing properly (sticky valve, allowed air in both directions) and the Charcoal Canister valve (line to fuel tank) was very sticky requiring a lot of pressure to open.

Throttle body cleaner on the PCV till it moved freely and same on the Charcoal Canister (while holding it upside down to make sure the fluid wouldn’t go into it) then compressed air and now that valve works a lot better (might replace it soon however).

After all this and dropping the Idle down to factory standard my problems have gone away while maintaining the low idle speeds (hopping when pulling up when the transmissions changes to first, maintaining 50km/h).

My other car (2000 Toyota Camry) also idles low when warm to i take it its a Toyota thing, didnt want to stray of the standard design spec if there ment to be like that etc.

Seems my Corolla relies heavily on these systems to run smoothly!

Thought i would update you guys on the progress in case anyone else out there is having the same minor issues.

[Author]

Replies