How long after cold start before the idle speed increases? The ECU will switch from open loop to closed loop in about 45 seconds, but it does that on a hot start as well.

 

The idle speed starts around 6-700ish on a cold start and it will take around 7 or so mins to reach high idle. Basically, once the jeep is warmed up. If I take it for a few mile drive and park it, the idle in Park/Neutral sticks around 1100.
While the jeep is warming up, the idle speed will swing its way back and forth to a higher RPM. My account is not exact, but for example: Cycles back and forth between 700-750 for a few, makes its way up to 750-800 for a few, then 800-850, and so forth until it reaches 1000-1100

 

I don't know how long it would take to set up the smoke checker, I'm thinking not too long through the brake booster hose. Have you tried smoke checking it after the engine is hot?

 

Forum veterans, feel free to chime in here!

 

Doesn't take long, easy to use. I'll go check again and let you know.

 

Ran it up to temp, and turned it off. The only smoke I saw was a small amount coming from the area of the TPS, and some coming out of the EGR. I imagine that some small leaks are to be expected, but nothing seemed too crazy. No smoke around the intake manifold, or TB base. In the past, I've tried spraying brakleen around those areas to no avail. I even tried soapy water earlier and no dice. I've plugged all the unnecessary vacuum lines and the engine still idles high. The only thing I can think of that is left, could be maybe a crack in my intake manifold? Or a compromise somewhere around the intake gasket (that I haven't found)? I know for sure that I have an exhaust leak because I have a ticking noise under acceleration. Whether the exhaust leak is at the gasket or somewhere on the header, I don't know. I tightened the intake bolts a few months ago, no change then, so I doubt there would be one now.

 

The smoke check would reveal a crack in the intake or a gasket leak. I'm leaning towards the butterfly valve in the throttle body, but I have no experience with adjusting that. Hopefully, someone on the forum with experience with that will chime in. What I can't rationalize is why a problem with the throttle body would cause idle to increase as the engine heats up.

 

That's what I was thinking too. Surely smoke would come out of the crack or gasket if there is one. The confusing thing is that the butterfly valve has a gap of about .0030", which (if I recall correctly) is what Cruiser54 specified it as being around. This is all around, a very strange problem. Say that the issue is a leak at the intake (whether it be loose bolts or a bad gasket), I'd think that the idle would be much higher than around 1000, and I'd think it would have gotten worse over the 2000 miles that I have driven the car so far.

 

Another long shot you could try, but it won't cost anything to try, is to turn the TPS down to 15% of Ref voltage and see if there is an effect on idle.

 

I checked the manifold bolts this morning, I was able to get to all of them except the lower one closest to the firewall. All are tight. I may try adjusting the TPS eventually, but if the issue is air getting somewhere into the intake, I doubt adjusting will remedy it. I may take it to a shop within the coming months to check it out. If the issue is ever fixed I'll update the thread as to what it was.

The only things left I can think of would be:
-Still an intake manifold leak at the gasket, or a crack (yet the smoke test doesn't show any, even when the engine is hot)
-Idle Air Control?

 

I just signed up here, but I live in So Cal too and have a 1990 Renix with the 4.0. My old EGR is still good, I’d possibly be willing to loan it out for smog or testing. Just so everyone knows though, I did find a NOS EGR valve from a little parts guy in Northern Italy. He shipped it DHL. Paid with PayPal and no issues. You have to check like eBay.uk or .fr, stuff like that to find the overseas sellers. Then just email them and ask them if they’ll ship it to you. I also have a couple of AC Delco 213-17 O2 sensors doing that. I check all the time for obsolete parts and just buy them to have on hand for the next 30 years.

 

This whole thread sounds eerily similar to the situation with my 1990 Renix XJ. It runs nice and smooth, but the high idle at stoplights ruins the effect. I recently got my hands on an REM and it is great. The check-engine light asterisk is on by the HT voltage which I'm unsure how to address.

 

Does it go into closed loop? After I replaced my O2 sensor it would go into closed loop almost immediately.
74Plb

 

To correct the vHT issue, try replacing the Oxygen sensor heater relay.

 

Tried replacing a few relays, to no avail. I think I need to dig deeper into finding more vacuum leaks. Is the vacuum tube to the brakes behind the firewall?