High and rough idle

March 29, 2016

Hello guys,

I have a 2005-06 Toyota Corolla 1.6 VVT-i 81 kW (110hp) hatchback with 3ZZ-FE engine (with electronic IAC valve). I'm trying to fight these both problems and have no luck. When the car is started in cold ambient temperature (below 0C/32F degrees in winter) the engine idles about 1600 RPM for about 4-5 minutes before it slowly idles down. What is more mystery to me, today it was 17C/63F degrees and on cold start it got even up to 1950 RPM.. And another problem is when the engine gets to normal working temperature, the idle starts to be rough. RPM's drops till ~600 and it sounds like the engine will stall but after few secs RPM's go up to ~750 (and everything repeats).

What I have tried to do:

*Changed the intake manifold gasket to the orange one;
*Cleaned MAF sensor, throttle body with IAC valve, PCV valve (would have changed it to a new one but it costs about 40$ in my country to buy it from the dealer..);
*Changed the spark plugs to NGK (recommended in owner's manual);
*Found a few DIY's online and checked the ignition coil and fuel injectors resistance (all are the same), so I assumed they are not the problem here;
*Checked for fault codes via mini-VCI (none found);
*Tried to find visual vacuum leaks (none), is there another way to try to be sure?
*Changed the serpentine belt, oil, oil filter, air filters (if they can cause these sort of problems).

I've included a picture of live data (got from mini-VCI) when the engine is in normal working temperature and is on rough idle. Outside temperature was 17C/63F degrees. Is air intake temperature 35C/95F degrees not to high? And air flow 1,45 grams/sec (0,19 lb/min) not too low? Maybe you'll see something out of ordinary here.

What should I try next? Any thoughts are welcome.

March 29, 2016

Hi,

I'm no sensor expert, but reading your post, the first thing your symptoms reminded me of is when you have disconnected the Battery , which clears /resets the ECU and when you reconnect and drive off the ECU has to "re-learn" and drives exactly as you describe for the first few miles.

If you have not disconnected the Battery intentionally, wonder if the ECU is loosing power some way ? Assume the Battery must be good as you do not mention starting problems ?

You could prove the point by disconnecting a minor sensor, to get an error logged into the ecu; leave overnight then see if the code is still stored, if it is then the ecu must have retained its power ok, so your problem must be elsewhere .....

March 30, 2016

9 hours ago, oldcodger said:

Hi,

I'm no sensor expert, but reading your post, the first thing your symptoms reminded me of is when you have disconnected the battery , which clears /resets the ECU and when you reconnect and drive off the ECU has to "re-learn" and drives exactly as you describe for the first few miles.

If you have not disconnected the battery intentionally, wonder if the ECU is loosing power some way ? Assume the battery must be good as you do not mention starting problems ?

You could prove the point by disconnecting a minor sensor, to get an error logged into the ecu; leave overnight then see if the code is still stored, if it is then the ecu must have retained its power ok, so your problem must be elsewhere .....

Thank you for your reply. Well the Battery is okay and there was no starting problems even in very cold temperatures (-23C/-9F) nor there is now when it's a lot warmer these days. About the ECU, when the Battery is disconnected it looses it's memory. But at the same time radio will loose it's memory too and speedometer trip information will be reset too (not the total mileage the car has run). And I didn't experienced any of these symptoms. I've checked the main ground cables and cleaned the ground connectors to the engine and car body (they were a little oxidised). But I don't know if ECU looses power supply will trip information reset? So I'll try to do as you say and write back here.

April 7, 2016

You should try cleaning the idle speed control valve. Its attach to the throttle body. Sometimes carbon builds up in the valve and it causes idle problems.