halik

Still trying to figure this one out - the car runs and drives fine and holds idle steady. When I first start it after a while (cold), it idles like crap for 1-4 seconds (600-800rpm almost like it's gonna stall) then the rpms shoot up 1200 and slowly drop to 1000 and everything runs great. I can rev the motor and it won't have any issues.

I've got a new dme temp sensor, fixed AFM (with that wiper mod), new vacuum lines (no leaks that I can think of) and the top end was totally rebuilt last summer.

Any ideas - maybe bad o2 sensor?

V2Rocket

idle valve

whalebird

Check-valve in fuel pump.

halik

Wow didn't even think of that. I had the pump and all the lines over there apart last summer, so replacing it will be super easy and cheap to eliminate it as a culprit.

whalebird

The fuel pump check valve is available seperatly from the fuel pump. You may have to dig around for it, but some will try to sell you an entire fuel pump. Good luck. If you continue to have problems, put a fuel pressure gauge on it and see if it is doing what it's supposed to.

Grandpa#3

Here is the link for the Fuel Pump Check Valve. The vlave prevents fuel from flowing back and keeps fuel at the fuel rail for your cold start.

http://www.pelicanparts.com/catalog/...ULinj_pg4.htm#

Cheers,
Larry

rude944

Replace the plugs recently?

halik

plugs, wires and all of the top end was redone last summer

944Ross

Almost sounds like some oil drools down the valves overnight and needs to be cleared out.

halik

The head I put on had the guides redone 40-60K ago and I've removed and cleaned all the valves. I really don't think the stuff is leaking.

Also I still have a bit of a weird situation when it's idling cold and i give it WOT - it stumbles/lags a bit in the low rpms (~1000) before it shoots up. Maybe the injectors are leaking?

Will Feather

FPR?

I have a somewhat similiar problem. When my car is cold or has been sitting, and I rev it up or try to drive for the first 5-10 secs it will bog and idle. I suspect my FPR.

supes6

I have the exact same problem. Replaced just about everything and it is still there... except for the idle control valve. I ordered a new ISV and fuel pump check valve, I'll let you know if that makes any difference. Also, I'm not sure if it's related but I've recently developed a hot start problem... starts eventually but it usually takes 6-7 tries after opening the hood.

944Ross

When you describe it that way, it sounds like my 84. I've always assumed it's the AFM with a bad spot, that is not enough of a problem when warmed up to be so noticeable.

black944 turbo

Mine does the same thing, I think mine is the check valve. Let me know how this works out.

supes6

I just finished replacing my check valve... also put in a new ISV. I tested it after putting in the new ISV and it didn't seem any better. Haven't had a chance to drive it with the new check valve yet but I'm pretty sure that was the fix.

The old check valve that I removed looked more like a simple banjo bolt - no spring mechanism at all that I could see. Since the PO had the fuel pump replaced only a few years ago, I'm wondering if they did the check valve at the same time but used the wrong part. It was definitely not the same as the new part I replaced it with.