divil

That is warmed up. It was always like that when warmed up. When cold, it's still exactly the same as the first video. It's not just the idle, it's the misfiring that happens at the lowest throttle setting, just off idle.

I just posted this that last video to show the difficulty I'm having setting the idle speed, which was recommended to try and solve the original problem.

travisgreen

What makes you think it's misfiring? Bc of the fluctuation in rpms?

divil

Well fluctuation is putting it lightly Maybe the video doesn't show it very clearly..but when it's cold, and I add throttle, the engine stumbles and almost dies - that's what I mean by "misfiring". Maybe I'm not using the term correctly sorry. But it sounds to me like it's running on 3 cylinders for a second or two, then it smooths out.

Then, when I release the throttle, it sinks back below the proper rpm for a second or two, and the stumbling happens again, and then smooths out again.

I think they might be 2 separate problems actually...the first one goes away after a few minutes, the second one hangs around for longer, but eventually it goes away too.

travisgreen

Ok, I'm just trying to figure out your concerns. From what I see in your 2nd video it appears ok. You will never get it to idle at anything without at least some fluctuation. The fact it's a 4 cylinder and you have the factory AFM it's going to fluctuate quite a bit, maybe not by sound, but actual rpms will never be at a set number. As far as your cold running problem it may be simple depending on what you have already tried. If you think it's running on 3 cyl at times when cold it very well may be. When is the last time u did a tune up? When your engine is cold it runs rich until it warms up, a weak spark could flood a cylinder when opening throttle body. Check the basics first. Do you have any way to monster afr?

travisgreen

Monitor

divil

Yeah the idle in the video is ok, I have no problem with it being like that. It's just that I can't set it with the kind of precision called for in the procedure that Rogue linked to (Clark's garage).

I don't think I mentioned all the stuff I have done to try and solve this already, so here goes - this has been over a period of about 18 months:

- new distributor cap/rotor/plugs/wires
- new DME temp sensor (tested from the DME connector also)
- injectors cleaned by Witchunter
- new O2 sensor (probably nothing to do with it when cold anyway)
- new fuel filter
- new air filter
- swapped fuel pressure regulator for another used one
- swapped AFM for another used one
- replaced all boost and almost all vacuum lines (except the AOS-crankcase hose and a couple of the tiny hard lines)
- cleaned all electrical grounds
- tried running with TPS unplugged (issue is the same)

I have been chasing this issue for a long time. When I say "new distributor" for instance, it was actually about a year and a half ago, but it was in an attempt to solve this same basic problem, and it had no effect. In fact none of this stuff made any difference at all!

BTW thanks for all the help with this so far, I do appreciate it.

Edit...no I don't have any way to monitor AFR.

travisgreen

Is it only doing it under light throttle when cold?

divil

Yes. The moment you give it more than the bare minimum, it revs up nice and smoothly.

travisgreen

Well it looks like you have dealt with it for awhile. If it was mine, I'd deal with it until I had my intake manifold off next and check your icv. That wouldn't be my first thing to check, but the fact you say it makes no difference in idle when you jump the icv is odd as it's usually pretty noticeable when done correctly. I'll keep thinking but I'd narrow that out first.

divil

When it's cold, jumping the idle valve makes a huge difference, it will almost die instantly. In fact it has a similar effect to adding throttle, maybe a little worse.

It's not too bad to live with, just a little annoying. If running with the AOS isolated from the intake gives any improvement, then the intake will be coming off pretty soon. Either way I will check the idle valve next chance I get. Another issue I've heard of is that the transistors in the DME that drive the idle valve can go bad, so even testing the valve isn't always definitive. I did test with another DME and it was the same, but who's to say that DME didn't have the same issue lol!

nofalls

Remember that when you press the throttle the TPS switches off the idle valve. So, the idle behaving similarly to when jumping the test port to disable the isv is not too suprising. Have you checked the TPS per Clark's? It might be wonky and not commanding the necessary enrichment at tip in.

divil

Yes I have tested the TPS. When I rebuilt the TB the other day I verified that the idle contact in the TPS works. But in the past I have also tested the full analogue range (which the DME doesn't even use AFAIK).

86 951 Driver

What about the coil? Usually they fail with heat, but it could be an issue.

divil

Well I just started it cold with the J-boot to AOS line plugged...no improvement. I am a little surprised given how badly air was leaking out of there under pressure. But at least I can rule that out.

Maybe, I'll have to look up some info on how to test it.

I think it's looking more and more like the ISV though. What throws me off is the fact that I know it works in some sense - when cold, it will give the car a fairly stable idle (as long as I don't touch the throttle). I know the ISV is doing this because if I jump it the car will immediately struggle to idle. So that kind of suggests the ISV is working to some extent.

On the other hand, I know it is used for more than just idling - it is used to somehow augment the throttle, but I don't know the details of that....is it used more at low throttle, or in a linear way throughout the range? The engine does occasionally seem hesitant or down on power a little, I wonder if this could all be connected to a bad ISV. If anyone knows more details about how the ISV is used, please chime in. I know it is just speculation but I have to wait until the weekend before I can pull the intake or do any serious troubleshooting, so I might as well have the ideas stacking up in advance!

nofalls

I was thinking that if the TPS was worn at the start of the trace and produced a bad or noisy signal then it might account for the poor behavior. Just a thought.