LP76

Yes I've read this too. The screw I refer to is behind the throttle arm, and appears to simply change where its resting position is. Is that the scree you are referring to?

I assume you mean bypassing the IAC valve by linking the two coolant lines together, yes? Won't that make the car just idle at around 1100rpm (which it does upon cold starting)? Also, I thought messing with an idle speed screw was generally frowned upon with an EFI motor? In any case, I noticed yesterday that there is a screw/bolt that appears to set the resting position of the throttle arm. Is this the screw you are referring to? When the car is idling well, and not surging, it stays around 750-800 rpm. This is a correct idle speed, surely? I increase the resting position of the throttle arm, that'll just make it idle higher won't it? Seems like an easy way to mask a problem, but creates another one by making the idle too high.

Ok I totally understand what you are saying. The surging is/was fairly slow; dropping down to around 400-500 over a second or two, then surges up to around 1100 over the same amount of time, then repeat, repeat... I checked the vacuum hose going from the the manifold to the fuel pressure regulator. Seems okay, no cracking present. I also checked the hose from the regulator downwards as far as I could without getting under the car/really clambering around to follow where it goes. I bled the coolant again with the rad cap off, and no bubbles came out. I also made sure a code hadn't been thrown after the stalling event, and of course there isn't one present. I dunno, I'm ready to give up. If it was a consistent thing it would be much easier to diagnose and fix, but because it so inconsistent, it seems like there is no way of trying to eliminate the potential problem through trial and error.

Okay will check the cable tomorrow. The idle surge has not been as frequent as of late, though one thing that has happened quite a few times is that when the motor is warming up, just after starting driving, it has almost stalled (and today it actually did stall) when coming up to a set of red lights. I notice it coming back down through the gears, going into neutral when finally coming to a stop. The revs drop almost to stalling speed (as I said, today it stalled once) and then surge back up before finally smoothing out. This has happened three times I think, and each time it has been after the car has been driven, stopped for a few hours, then driven again. Once it's warmed up to full operating temp it doesn't happen. It's very strange. I'm starting to think I should maybe just sell it and get something else, as I'm pretty over it. Aside from this ongoing problem, the car is great, but the problem irritates me enough that a lot fo the time I wish I had something else.

Hi again. So, I ran the car from cold to hot, and then for an extra 10-15 minutes, with the rad cap off AND the heater on (which I forgot to do last time). Numerous bubbles came out when the motor became warm, and then finally stopped after several minutes. Could this have been the cause of the intermittent idle surging? I might re-iterate that the surging is not always present, and starts and stops with no apparent rhyme or reason. More annoying to me is the dead spot at the very beginning of the throttle. It is small, but definitely present. Surely it is should not be there?

So, literally just close in the hole in the bottom of the throttle body (the one that leads to the ICV) when it's running? Problem is, every time i go to solve this fucking problem, the idle is fine!

I did run the car with the rad cap off a few days ago, with no noticeable bubbles coming out over a period of 10-15 minutes of running, from cold to warm. I can't see how you could possibly jack the front of the car up enough to make the radiator cap higher than the throttle body though?

Pulled the PCV valve again and checked it - seems fine. Can blow through it one way only. Sprayed carb cleaner all over the chamber to manifold and manifold to head interfaces - no noticeable change in revs at all. Of course the car was idling just fine when I was checking these things again though. I'm out of ideas.

Also, for the manifold gasket, I assume the one between the intake manifold and the engine, not the one between the intake manifold and the intake chamber?

Sorry, I should've been more succinct. I meant that the PCV didn't appear restricted in that I could definitely hear the "rattle" when shaking it, and from memory I could only blow through it in one direction. It's easy enough to access though I suppose, so will double check. I checked the coolant level yesterday. Still as good as gold, and running the car with the cap off didn't produce any noticeable bubbles. The thing I don't understand is if it is indeed a vacuum leak, why would the symptoms not be present all of the time? Anyway, it's a bit too dark to muck around now, but will try pointing some carb cleaner at the intake manifold tomorrow evening and see what happens. Will be reporting back. Cheers again folks.

Am I able to detect a leak at the intake gasket with the motor running by spraying with carb cleaner or soapy water? I've never removed an intake manifold before, and am a little hesitant to do so. Pushing the brake makes no difference. I had the PCV out a month ago; inspected and cleaned it, it didn't appear restricted. The surging (revving up to 1100 rpm or so) happens immediately after the idle drops down to 400 or so. It doesn't all of a sudden sit at correct idle and then go straight to ~1100; it's always a noticeable drop down first, THEN a spike up. And there is a small, but definite, flat spot right at the beginning of the throttle. Thanks for your help.

The car had some other work done at the mechanic a few weeka back and I got him to check the throttle problem as described. He removed and thoroughly cleaned the throttle body and the IAC valve. There was no noticeable deterioration of the gasket between the throttle body and the intake. I got him to check the error code 31 I had previously detected, but it was no longer present. I assume it had been cleared after my previous attempts at cleaning the throttle and various valves, which I described earlier. When the problem arises, which is intermittently as I mentioned above, the idle fluctuates slightly between ~600 and 1100rpm. It never stalls or goes much higher than 1000. The most annoying part is the small dead spot at the start of the throttle. I inspected all the vac lines last time but couldn't hear/see/find a leak.

Turns out the dreaded problem I described never actually went away. I thought it did, but is still occurring intermittently. Most noticeable when car is cold and starting to drive. Small dead spot at the beginning of the throttle, and jerkiness when driving at low rpm until the motor warms up a little.

So, after all the mucking around, the car has settled into a nice idle, no hiccups, surging, or hunting, and most importantly, no dead spot in the throttle. I didn't end up bleeding the coolant system, so I assuming that it was one or more of the components that I cleaned that were causing the problem. Thanks very much to all who offered their opinions and time. Now, to replace the rear shocks....

Okay, will give that a go. Cheers.