Hello folks. I hope you can help me with my friend’s car. It’s a '95 Toyota Paseo (I believe the same engine as a Tercel).
It had an oil leak, which I found to be the camshaft oil seal. In replacing this, I also replaced the timing belt. Other recent work: new spark plugs, new distributor cap & rotor.
Before I did any of this work, the car had a problem where it would lose power during moderate to hard acceleration. I decided I would not mess with that until after the oil leak was fixed.
Anyway, after I fixed the leak and put it back together, I started it up and it ran like a champ! Even the acceleration problem was much better. I attributed this to a stretched old timing belt, which must have thrown the timing off enough to cause that problem.
BUT! Then I found out that after the car warms up to operating temp, it has a WORSE problem now. Now, the engine stalls (and sometimes completely dies) after the accelerator is RELEASED. So if you rev it up, then let off (either gently or abruptly), it stalls or dies.
I have the factory repair manual, and have followed steps for troubleshooting the MAP sensor circuit. The MAP sensor is behaving normally.
The only other cause the manual lists for such behavior is an EGR system problem, but EGR only came on California cars, or cars with an auto transmission. This car does not have an EGR.
So, the last step in the manual flowchar is “Try another ECM”.
Is there anything you guys can think of that I am overlooking, before ordering a new computer?
Any suggestions appreciated!
Before I replaced the ECM, I would make sure that the Idle Air Control (IAC) motor is working correctly. This is what allows the engine to idle correctly. Try cleaning the throttle body with emphasis on the idle air control passage. It is possible the pintle is gummed up and sticking once the engine is warm.
If the engine does not have an air leak then it could be the Idle Air Control valve as mentioned. The IAC is a controlled air leak, at least in theory. 
How did you set the ignition timing? There is usually a test connector that must be grounded or jumped before setting the timing.
Failure to do so will throw the timing way off and it can also cause a problem like this.
Following the factory manual, I used marks stamped on the engine to align the crankshaft and camshaft when replacing the timing belt. As I mentioned, before it warms up it runs very well. Only after 5-10 minutes of running does it behave badly.
I’ll double-check the timing to make sure it hasn’t gone funny. And I will check the IAC and clean the throttle body.
Thanks for the suggestions! I will post after I try these steps.
Hope everybody had a fun July 4th.
I checked the timing on this car and adjusted it slightly. It was running at about 15 deg. BTDC, and specs called for 10 degrees. After doing this, I revved the car a few times and the stalling problem seemed to be gone! I was able to drive the car, and it ran like a champ again.
I was very excited. But, when I got back from driving for about 30 minutes, and came to a stop, it started idling badly again. This time it did not fully die, but the RPM went from 900 to about 400, then came back, then about 30 seconds later repeated.
I checked the timing again and it’s still 10 deg, but the car seems to be idling badly because the timing mark drifts at idle, between about 8 degrees and maybe 12.
What could cause this?
Side note: I cannot find the Idle Air Control valve… I know what one looks like after finding it online, but the parts databases only seemed to offer one for an AUTO transmission. Is it possible that a manual does not have the same valve? Or, where is it that I’m not looking?
Any help much appreciated.
For me, it’s a coin-flip about which component could be at fault. It’s not just engine temperature change, because the problem occurs after 30 minuets. You should follow your Haynes or Chilton’s manual and check ALL the sensors and control valves with a multimeter. If you put a vacuum gage on the engine while it’s running, it would probably show the vacuum swinging. But, is the poor idle causing this, or, is there a vacuum leak? Hard to tell. The iac (idle air control) valve is probably attached to the TBI (Throttle Body Injector) housing. It has three hoses attached to it. I wouldn’t change it without cause. It’s pricey at $124. + If the check engine light has come on, read its flashes. The connector to jumper is probably under the hood. The ecm may flash a trouble code even if the check engine light doesn’t come on.
It sounds like a fault in the electronic spark timing system (or knock sensor) system.
Have any fault codes been set?
Check the knock sensor. If it’s malfunctioning and sending irratic signals to the ECM, the timing will fluctuate.
-Matt
Sounds like an Idle Air valve problem. The car should have on that looks like this and should be mounted on the throttle body near the throttle lever:
http://cgi.ebay.com/ebaymotors/IDLE-CONTROL-VALVE-TOYOTA-PASEO-92-95_W0QQcmdZViewItemQQcategoryZ33557QQihZ013QQitemZ230149269634QQrdZ1QQsspagenameZWDVW
Sometimes removing and cleaning them helps and other times it may need replacement.