irregular idles

[180fan]

Alrighty so I've got an irregular idle. I get a range of 750-770's in neutral then I'll get the occasional pluge to 680 then it'll bounce back. Now when I'm in gear and just beginning to go, I'll see it go to around 600 or dip to 550. I've cleaned the AIV, cleaned the intake piping and manifold (as best as I could), and have also tried playing around with the idle screw. Perhaps there's a small vacuum leak? But if that's the case, why does it dip so randomly? Or is there something else more fundamental I'm overlooking? Any suggestions? If it is the vacuum lines, would you recommend replacing all the lines and if so what size diameter are they? I think some of them are about 10mm, and 5mm from what I could eyeball but does anyone know for sure?

thanks in advance

[NISTECH]

does it appear to be loosing a cyl(missing) or does it just gradually slow down then pick back up?

[180fan]

The idle just drops for a second then picks back up. It's not like it's a constant drop, but it's fairly random but at the same time I can expect to see that rpm dip every minute or two.

[drift-sx]

maybe you jsut need to ground your engine, or ground it better. Search grounding for all the locations. This can be done with generic wiring and tools, not hard to do

[180fan]

yeah I've already started to add some extra grounds. It's strange though, never seen anything like it. Right now just to help alleviate the idle, I've got a bit of a fast idle now. I think I'm gonna give some more fuel system cleaner a shot see if that helps any. For sure though, I'm thinking about adding another ground to the throttle chamber, somewhere on the intake manifold, replacing the ground strap that is towards the back of the engine near the exhaust manifold and transmission ground. Gotta think of some more places to do the grounds...I'm thinking also about going back to check on my aiv and cleaning that out again.

[MikeMurphy]

throw in some new plugs, and check your spark plug wires for cracks since it only takes 2 seconds.

What the milage on your engine? You may have some throttle body plaque which could have an effect on it. Maybe some dirty injectors?

Still persists then check out your distributor for signs of uglyness.

Sometimes the clutch cylinders eat some power up when in use so it may dip a tiny bit for a moment when engaging the clutch.

im just thinking out loud here. dont listen to me, im stupid.

[180fan]

well the spark plugs came to mind today. I checked them all out, all golden brown. So I know I'm getting combustion. Then I checked out the fuel lines to make sure I was getting clean gas. It came out clear. Possibly the fuel pump? Since it is an 89 with about 163k on it now. I think it'd be a good idea to replace all the vacuum lines anyway even if they're not the culprit as I'm seeing cracks in them. I just need to find out what the hose sizes are. I tried cleaning the throttle body again this time I just hosed the manifold and started it right up. Stuttered like crazy until it was all burned off, but came out smooth. But later in the day, the problem still persisted and actually the dip got a bit worse. Now it teeters around 530 rpm at it's low but with more driving it gradually goes up. Perhaps my fuel pressure regulator's gone on the fritz? I popped off the line after the fuel fliter just before the hard lines just behind the intake manifold.

so my suspects are:1. fuel pump on the fritz2. regulator's decided not to regulate well

[sil80drifter]

I have a VERY similar problem. It started recently, almost insync with my fuel injector leaks. It dips as badly as yours, but then comes back up. Sometimes it's rock steady, sometimes around 800-900, sometiems it goes down to 600 and car starts shaking... I hope it's my injector, the one that's leaking that's causing this. I hope it is, because I'm getting new ones soon, so if that doesn't help... I'll do the grounding thing.

sil80

[vangj]

I'm having similar problems also. I have a SR20DET. Sometimes, mine is up; drops, goes back up, drops again and so forth. Sometimes, it idles fine, but at a higher rpm. Sometimes, it doesn't catch itself so it dies. I'm still trying to find out the problem. I was told to try unplugging my o2 sensor to see what happens. I was told that it might be my O rings for the injectors. I might have to check that also. It doesn't seem like it's my MAF's. I unplugged it and it revs that same, no change...