Amadeus

I hope someone can shed some light on this. I have had a couple of problems lately that are now gone; intermittent idle and fuel trim malfunctions. Early on I removed the IAC, cleaned and reinstalled it. The problem did not go away. Later the fuel trim code would show up about twice a month. I figured that I had some sort of sensor problem and ignored it all until I could schedule some quality garage time.

I finally got some and a quick visual inspection revealed the hose connecting the plenum to the TB had fallen off - possibly due to an improper installation when I changed the PS hose about a month, or two ago. I could not get my hands in there to put on a new hose, so I removed the plenum. Well, in there was a large amount of sludge sloshing around. I cleaned everything out. Before putting it back together, I read up on what this stuff was. Looks like the missing hose is unlikely to have been my problem. I found a few posts about how this is supposed to keep sludge in check, but the system fails early in the 12Vs life. Rats.

So I put everything back and get ready to look for the real problem. During installation, I find sludge in the TB. I clean it out as best I can without removing it. Button everything up, check a few simple items and give up for the night.

Well, that was about three weeks ago. The idle problems are gone, and I have not had any fuel trim errors. In general it seems to be running well.

My theory:

Sludge had built up to the pint where it would occasionally be slurped into the TB, wreaking havoc on the system.

Supporting evidence: I clearly recall almost stalling a few times when breaking hard, but it would run fine soon after. It was more likely to through a fuel trim code when going down a steep hill. It reminded me of a carbureted vehicle having float problems.

Am I crazy?

VAP

goes inside the IM and lays on the floor or clings to the walls. There's simply not enough velocity to pull oil solids into the combustion chambers. If there were our IM's would be shiney and clean inside as everything would be sucked into the combustion chambers rather than clinging to the IM internal walls and floor like it does. Gravity dictates everything heavier than air in our IM sucks south!

With fuel trim issues I'd personally be looking at things like O2 sensors, age, mileage and if OEM or generic/universal. Fuel injectors dirty/partially clogged, vacuum leaks, intake leaks, dirty MAF sensor wires, FPR issues or bad EGR-to-IM gasket/loose bolts and those CCV hoses if broken, cracked or disconnected absolutely WILL cause a fuel trim code due to unmetered air. Anywhere unmetered air can get into the intake tract can and will throw the code. Fuel trim levels are almost always related to bad O2 sensors/faulty signals or unmetered air in the system. If the air is a large enough volume that "fuel trim" code will convert to an "unmetered air" code. And unmetered air will certainly cause irratic idle issues. Just pull the small hose off the TB that goes to the charcoal cannister purge valve while engine is idling to see evidence of that first-hand. Small leaks and it idles roughly. Large leaks and it won't idle at all tho it will start but takes small doses of "go-pedal" to keep it running and even then it runs "roughly."

These engines are VERY picky about wanting 100% of their combustion air to come in via the airbox and "thru-the-MAF."

Amadeus

Rats. Well, more stuff for me to check then. Something must be loose. Thanks for the info.

dorsal900

And now everything is better?

FYI, if you still have the original Valeo AIC valve, you may be on borrowed time and stalling may reoccur. I went through two of these (cleaned a few times before failure) before Bosch came out with an improved version, which has been on my 1996 car with NO ISSUES or cleaning for about five years.