Erik Hoeffner

Hey guys, got a small issue I can't seem to figure out.
I recently put a post 99 intake manifold on my Jeep. Power and throttle difference is obvious, sounds fine, runs fine, and the RPMS are normal in reverse and drive (3 2/1) But then when I put it in park or neutral the RPMS stick around 1000 or 1100.
I have drained the computer 3 times to let it reset, Idled for 5 mins the first time, 2 mins the second and this 3rd time let it idle for 10 minutes to see if that would help, still the same.
I drove it "average" all three times, I thought after a drive the first time the idle would fix itself, but nope.
So I'm thinking maybe my idle sensor when bad around the same time I swapped this in? Thats my only conclusion so far.

...What is odd too though, it seems to idle fine on a cold start (6-700ish), sitting over night type cold start, but then as soon as I drive a bit and park it again its back up to the 1100 level.

Anyone had this issue with the newer manifolds, or do I have a bad sensor??

Mendax13

vacuum leak?

salad

Sounds like a vacuum leak to me too. Go around and tighten all the manifold bolts again. Also, do you have an aftermarket header? A number of them are known to rub against the '99

Erik Hoeffner

Hmm ok. I don't have an aftermarket header, I wish I did, probably bring in more power... But I do have another thread on here I just posted, regarding all my heat and air coming of the defroster. People on there are suggesting vacuum leaks as well; idk if that could be connected with a manifold leak though. Would this affect my power at all out of curiosity?

EVILXJ

vacuum leak

salad

Affect your power? Slightly positively as there are fewer restrictions on air entering the engine. The vacuum is created by pistons sucking in air. If it doesn't come from the right place things don't work properly.

After you tighten up the manifold bolts, walk around with some carb cleaner and spray lightly around the manifold and any vacuum fittings. Listen for a change in idle. It would be a good idea to have a fire extinguisher nearby in case things go awry.

Erik Hoeffner

Well fer sure, I will try to get to tightening those bolts this weekend, if its warm enough; kinda don't see how they could be loose, as I had tightened them to torque specs, and it was installed after replacing the head gasket, so there was room to move and make sure things were seated right. On that note, that is why I am confused of any vacuum leaks. All hoses had to be disconnected and reconnected and they were all in decent shape or replaced and fitted well.
I guess it is possible the bolts loosened after heating up? But it had high idle from the first start after finishing the whole job, if I recall properly.

...And how awry could it get..?

Mendax13

it might not just be a loose bolt but any part of the vacuum system. that is leaking or open.

freegdr

Iac stuck ?

Erik Hoeffner

Well I llooked it over last night, I saw no broken vacuum lines or any disconnected, so...and I suppose the IAC could be stuck, but why is the idle fine on cold starts?

mdnov

It may be due to a richer mixture.

Mendax13

possible for it to be the Throttle position sensor? maybe, i dont know if that could do it dont know much about those parts

freegdr

Missed cold start part have you read codes see what it says ?

Erik Hoeffner

Haha yeah, all I got was a 17 "engine running to cold". Dumb.

stang65

have you adjusted the idle screw. I had to on my throttle body after installing it.