Idle and driveability problems
 

I have a 1996 LE 2.2 liter automatic with 232k miles. It has been our workhorse and a big part of the family. Other than normal maintenance and expected stuff wearing out, it has been a trouble free car.

About a month ago it started to idle poorly with a weird rise to about 1800 RPM then drop down and usually die when in Park. It would run very rough sometimes and have a flat spot when pulling away from a stop and sometimes die without warning. It would run great then after it was parked from between a few minutes to about an hour it wouldn't start. Try it again in an hour or so after that and it would start right away. The car has never thrown a DTC code (Check Engine Light). All the misbehavior seems to happen after the car has gotten to normal operating temperature. Otherwise it doesn't seem to act up the same way every time. With the help of a general mechanic friend of mine and the shop manuals, here are the things I've done so far:

• Replaced the big intake hose because it had cracks. Since the 4 cylinder cars don't have an MAF (Mass Air Flow) sensor, this probably didn't affect the driveability problem too much other than to make sure that only filtered air reaches the engine.
• Checked all the vacuum hoses I could find for leaks and they all tested good
• Checked the MAP (Manifold Air Pressure) sensor and IAT (Intake Air Temperature) sensor according to the Toyota shop manual and they checked out OK
• Checked and cleaned all the electrical connector plugs and grounds I could find and all were OK
• Had the ECM (Engine Computer Management) computer tested by an ECM specialty shop and it tested out very good. In fact the tech was amazed at how good a computer could still be after that many miles/years.
• Checked the EGR (Exhaust Gas Recirculation) valve and it appeared to not be operating properly. As an FYI, I learned that you can detach the vacuum hoses from an EGR and the car will still run but if it runs better with the hoses detached the EGR is probably bad. I replaced it and that made a very big improvement. It seemed to have solved the no start (after a few minutes to an hour's time) problem and it ran much smoother but it still wanted to die at bad times and the idle would still vary by a big amount.
• Next the IAC (Idle Air Control) tested OK but the recommended test is pretty basic. Apply 12 volts to the electric leads to see if the IAC valve will open and close. It did but given the other symptoms it was decided that it was the next thing to replace. After I replaced it, most of the flat spot and dying at stop signs, etc. went away but not completely.
• I'm sure there are some more things I've done to it but I can't remember any more

Even with all the improvement, it still does the sporadic idle, it has some, less pronounced, flat spots and a little bit of that feel that it wants to die all of a sudden. It hasn't died completely though after replacing the EGR and the IAC.

I am resigned to the fact that at this point I may just have to continue throwing parts at it. I hate to do that but given that the first two attempts seemed to help so much it may be my best hope. At least the car doesn't feel as dangerous to drive (if I'm driving it) but I would like it fixed completely because it is usually my wife's car and she wants it back. She isn't a car person so she should probably not be driving it if she has to make any quick decisions.

If you guys were me, what would you try next?

Ttt
 

Bump for some more smart guys getting home from work.

Was the replacement IAC new or used? If used, clean the valve.

When you changed the EGR did you inspect the exhaust plumbing to make sure it was free of carbon?

The EGR system is off at engine idle. If engine runs better by manually disconnecting the system at engine idle this is a problem.

You state the problems only occurs when engine is warm, if so check the coolant temp sensor for the computer.

Answers and thanks
 

The replacement IAC was brand new but, yes, I did try cleaning the original IAC, too, which didn't change anything. Forgot to mention that.

No I should have mentioned that the disconnected EGR didn't make much difference at idle. It was the other driveability problems (starting, stalling, flat spot) that seemed better when it was disconnected.

Can you point me to the coolant temp sensor? I don't remember seeing that in the manuals.

Thanks.

Follow the top radiator hose to engine. Sensor is on the coolant manifold and has two wires green/black and brown.

Thanks
 

I'll look for it and report back.

Eureka!!
 

Thanks to you guys for your help. I replaced the ECT with a high quality after market part (about $18 at O'Reilly's). All the remaining symptoms have gone away. I only drove it for about a half hour, finding all the conditions that it misbehaved before, so I don't want to be too optimistic but given the improvement the ECT was definitely involved in the problem.

I am still convinced that the other parts (EGR and IAC) were marginal to failing at best so I don't feel bad about replacing them. But this is such a relief and I appreciate your help!

The car now runs OK?

Yes!
 

It is running MUCH, MUCH better. :) It still exhibits a little roughness at idle but I suspect a timing issue rather than anything else with emissions or carburetion. I noticed a little rougher running after I replaced the timing belt recently. It was as close to right on with the timing mark that I could get it after about a half-dozen attempts so I didn't see how it could get any closer after that many tries. Power and fuel mileage have always been excellent.

What it does is run a little rough during a stop but when you put it in Park or Neutral it smooths right out. Plus it doesn't always run as rough all the time. When it idles after it is warmed up it stays at a pretty consistent 800 RPM according to the tachometer whether it runs rough or smoother. When I put it in Park it runs up closer to 900-1000 RPM. I suppose it could be that the idle is too low but I don't know how to adjust that or if it can even be adjusted. Thoughts?

There is no idle adjustment. The screw is to position the throttle plate opening and is factory set, suggest not adjusting it.

How did you set ign timing?