Hey guys:

I've been out of the Volvo scene a while, but recently jumped back in with a 1988 760 turbo wagon with about 175,000 miles on it.

I've been going over it preparing to start driving it daily, which has consisted mostly of replacing bulbs, cleaning, servicing etc.

One thing, however that is causing me a big headache is that I can't get it to idle well. Actually, it'll idle, but there's more to it. Here goes:

What happens is this...hot or cold, it will start, rev up slightly, continue to run a few more seconds, then drop down sharply and stall. Sometimes, it will catch itself before it quits running and stabilize, but that's not common. Sometimes, when it is HOT, it will start and idle evenly and not stall but that also is not consistent.

When it is idling, it runs slightly ragged...in other words it sounds like it's varying the idle about 25-50rpms. Not much but enough to detect if you pay attention. It also idles more slowly than it should and will not respond to the thumbscrew.

Before I touched anything, it would start and stall consistantly, but I could manage that by supplying more bypass air with the thumbscrew. I'm too OCD to live with a fuel-injected car that has to be feathered like a carburetor,so here's what I did to go after this situation:

First, I pulled the idle stabiliser, which had some oil in it. I cleaned it and tested it. It works perfectly in each directly, so I am confident the idle stabiliser is able to respond.

Next, I removed the hoses on either side of the stabiliser, the rubber hoses between the MAF and turbo, the oil vapor line between the separator and intake elbow, the rubber hose at the throttle body and inspected them MINUTELY for any splits or holes, and found none. I cleaned them all, replaced the oil vapor line, added clamps where there were none before and satisfied myself there were no leaks to be found.

I inspected all the vacuum lines, trimmed/replaced a couple that were marginal. I also adjusted the throttle body exactly as instructed here in the FAQ. One thing I DID notice is that the throttle body appeared to be adjusted far enough open that the TPS was past the point of clicking, eg no IAC command. I have that adjusted to spec now so that it clicks immediately off idle. My feeling is that this idle situation has been long standing and that was a workaround. I also noticed that the engine idle no longer responds to the thumbscrew AFTER I adjusted the TB!

Lastly, here is a description of the weird way the car ran on the first start after putting everything back together:

It started right up, idled at a fast (~1500) idle for several seconds, started drifting slowly down, then abruptly dropped to about 500, bounced back up and idled up and down for at least a minute. It spent the next 5 minutes with the idle freaking out. It would idle up and down, then all of a sudden race up to about 2200 rpms, hang there for 20 seconds, then drop back off a cliff and do the 500-1200 bounce. That was without touching the throttle at all.

Finally, I gave it a small rev, and it stalled immediately afterward. Since then, it has been on this weird low(650)rpm idle with no repeat of that freakout. The engine runs good otherwise, boosts normally.

One last detail i noticed is that the engine will not start unless my foot is off the accelerator. If I try to start it with my foot slightly down it just spins over. let off the gas and it finally starts.

So, I apologize for the novel, but I believe in supplying details. Thank you so much for any advice.