Hi
I know this has been covered, I did a search. I also read all the 700 informational sticky. My wifes 88 wagon has a fluctuating idle problem. It moves up and down about 2-3 hundred rpm. These are the things I have done.

Cleaned throttle body.

Ran a can of BK thru the car.

Major tuneup last year before smog. Plugs, cap, rotor, fuel filter, air cleaner.

Replaced fuel pressure regulator with another used one.

Checked vacuum hoses. Replaced most of them.

Checked injector seals, intake gasket,throttle body gasket, air intake hose connections , breather hose (fire trap) by spraying throttle body cleaner around them. No change in running. Doesn't appear to be any vacuum leaks.

Checked and replaced aux idle air valve with good unit from turbo parts car. I cleaned it before installing it.

Replaced fuel pump with another unit

The idle still fluctuates. After I replaced the main fuel pump today, I started the car. For about the first 10 minutes, I thought I had fixed the problem. The engine idled perfectly. Then the fluctuation started. It didn't seem as bad as before, but it was still there. The fuel pump came out of a turbo car and was only about a year old when the car was totaled.

Has anyone have any other ideas on the cause? The car has 280,000 miles.

Thanks Brad

Sometimes the throttle bodies can warp over time and not seal very well when closed. Also could be a worn wobbly distributor shaft.

It seems to me like a fuel delivery problem. Almost like a slight surge. After the pump switch, the idle seemed better, but not 100%. I can't understand how the TB would warp, unless subjected to some extreme heat. The car didn't have this problem when I purchased it and it has never over heated since I have had it. I was thinking maybe the TB shaft is sucking air on the TPS side. It looks as though it would be almost impossible to test without taking it all apart. I have been trying to resolve this issue for a long time and nothing has fixed it for more then 10 mins. The dist shaft is an interesting proposition. I have a new distributor, I will have to see if it is interchangeable. The dist is from a 89 turbo and the car is an NA 88. I know there were some differences in distributors, but can't remember the dates and models. If some one has this let me know? Thanks Brad

Don't have any ideas- just wanted to say I have the same issue with my 93 245 - Exactly! And I have done the same things as you.

We should start a club, maybe get t-shirts made up.

Do either of you guys, when the idle is fluctuating, ever hear a random occasional "putt" from the exhaust?

For what it's worth, I've replaced about everything but the fuel pumps, which seem fine. Done this since I put the motor in 20K or so ago.

Maybe we should. I have been trying to resolve this problem for a long while.