bought a 88 740 turbo that needed a few things; intake manifold gasket ( which was leaking really bad), fuel pump relay and a new connector (insulator) for the pickup/sensor in the dizzy.

It ran really crappy, the manifold gasket was the biggest, but it had problems starting while testing other things, a new dizzy was put in, did the manifold and wouldn't start. replaced the main relay and it started consistently. put back in the old dizzy with a new connector still started every time.


so, I go the thing running, did an emission test which it passed, and it drove, but idled erratic and rough. I work in a shop that specializes in volvos, but I'm not a master volvo tech yet by any means, so I did a bunch of things I know go out to make it dependable; both fuel pumps and filter, timing belt and water pump, belts, air filter, cleaned TB, cleaned oil trap and resealed, tune up.

I'm going overboard with details. my idle stays at 1000-1400rpm and I can't get it to go down for anything. I have access to michell, etc. and did the base idle adjustment, with the screw all the way in it still doesn't idle down. disconnecting or grounding the iac does nothing.


what is interesting is that I found 2 vacuum leaks last night. 1 is the nipple in the pipe from the maf to the turbo inlet and 2 the throttle shaft. I tryed blowing propane in those areas and it didn't change the idle.......


I see a lot of bad idles on this forum with no fixes.

 

I wish it weren't true.

I did not see you listing the Idle Air Control valve as having been tested or replaced. One thing you could do to see if the IAC is stuck open is get some hose clamping pliers and clamp it off.

That's a start. Good Luck.

 

You may work at a shop that specializes in Volvos but odds are rwd's aren't their forte. Just no money in 'em anymore...not enough on the road. Take a pair of hose clamp liers or, if you don't have a pair...a set of needle nose Vise Grips and pinch off one of the 2 hoses going to the IAC...when your idle instantly drops, you will have located your issue. Seems like you're off to a good start on getting your car back to stage zero. If I might make a suggestion: Replace every single vac hose. FPR hose, booster hose, charcoal cannister hoseclimate control, cruise...all of them. They carry positive pressure under boost and often leaks will only present on the road under boost. You can run a smoke machine, propanr...to your heart's content in the shop and never find 'em all. It's a safe bet you have bad ones you have yet to find. Additionally, assuming cutting air flow to the iac drops the idle, you'll have to find the specs on checking the iac. It may just be dirty...I remove 'em and clean them out w/ brake fluid.

 

I tried clamping off the hose going from the IAC to the intake and it doesn't stall with that black screw all the way in. though that doesn't mean the iac itself or the 2 lines going from it aren't leaking. I'm thinking about getting a hose and bypassing the IAC completely and then play with the throttle stop, and get it to idle at 750 then put things back on one by one and see if I can't deduce what's wrong with it.

I started working on mostly honda's, but I've done a bit a work on the parts of cars that make a RWD a RWD. Trannys are way easier.

like I said the idle doesn't drop when I pinch off that line.

a smoke machine works great at finding leaks especially if you block off the intake. but yeah I really should just replace all my vacuum lines. I replaced a few but not them all.

with the propane I'm attempting to see if the idle changes/starts running smooth from air leaks. cause I'm smoking more volvo's and see a lot of leaks in throttle shafts and intake boots that I don't think your seal 100%.

 

If clamping of neither of the iac lines alters idle you definitely have a vac leak somewhere. I've spent hours...literally hours on my 84 760T searching for vac leaks. I ended up buying silicone vac lines, replaced every single hose and cured it. Turned out I had a handful of tiny cracks that I couldn't see until I had the hoses off and in my hand. Also, there's a remote chance the idle circuit in the ecu has gone south. I've had that happen. 541 ecu's are still plentiful on ebay...I even have one listed!
http://cgi.ebay.com/ebaymotors/ws/eB...#ht_500wt_1182

 

I need to do some more testing and replace all the rest of the vacumm lines and I'll report back.