Still having high idle problem on 88 Jeep Comanche (4.0l)

Well, I got in there with a brush and solvent, and took off some stuff on the sides (beside the butterfly valve, for lack of the technical phrases). But it's opening and closing easily, and it's stopping when it hits the metal stop on the outside of the throttle. But is it perfectly clean? No. Should I scrub some more?

Clint

Scrub till you'd eat from it.

Carl

Have you cleaned the throttle body? It's real easy and will eliminate that as a source of the problem. Oil in the CCV system doesn't help either, and cleaning the orifices is in principle also easy.

Earle

Agreed. The IAC too. (Idle Air Controller). This can get jammed with tiny amounts of deposits. I would probably use carburetor cleaner.

Earle

When our 88 does that, I pull off the electrical plug to the TPS and give it a spray with contact cleaner then am usually good to go for a year or more before it needs it again. Electronic contact cleaner is the best, but WD40 will work.

That works every time on ours.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail > So I'm getting good vacuum using the very imprecise "finger over the

I've tried cleaning the contacts on the ISS and TPS with electrical contact cleaner and a toothbrush, with no change. Forgot to mention that.

Clint

I'm thinking it may not be too easy to haul the throttle body off, but I'd imagine that would make it much easier to clean properly?

Clint

BTW, this problem SEEMS to have started about the same time as I hauled the old radiator and water pump out and replaced it. Could very easily just be coincidence, though. I've tried checking all the vacuum hoses in particular around the area I was working in, but nothing popped up.

I'm tempted to head out to a wrecker, and see about snagging an old throttle body (preferably with sensors), just for S&G. Give me something to swap out some parts to try seeing what's wrong.

So it's not seeming that bad CCV valves/hoses should be causing the high idle, though?

Clint

It's only four bolts that hold the TB on, and the cables. Takes about 5 minutes to pull. Don't loose the cable clips, and be sure you make a note of what cables go where.

Carl

That's the thinking. The theory is that your IAC has carbon in it, which is making it function improperly, which is what is messing with your idle speed. Cleaning the contacts for the various sensors mentioned can help too.

Earle

God Bless America, Bill 0|||||||0mailto: snipped-for-privacy@aol.com

This is probably a really dumb question, but how do you remove the linkages from the throttle body? Some of the posts I've seen indicate it may just be a simple ball/socket joint, which means I just didn't use a big enough hammer (figuratively speaking, of course) on it. Thought I'd check in here first, though.

Clint

You are correct about looking for a vacuum line loose.

The CCV, if pulled off at the manifold will cause a steady high idle, but normally it gets blocked which just pukes oil into the air filter. It would be worth inspecting the rubber grommet where it enters the manifold for cracks though.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail > BTW, this problem SEEMS to have started about the same time as I hauled

No clues for getting the linkages off? Should I just pry a bit with a screwdriver?

Clint

Well..... sort of.....

You have to pull it off perfectly square with the backing plate on the TB or one side of the clip will usually snap off. Old spring steel and the slightest corrosion..... When you snap this clip, you can do a decent paper clip bracket to hold it back on or you need to buy new linkage... My 86 CJ7 has the paper clip fix thanks to Bill H.

I will go look at the 88's to make sure it is the same.

OK, nope, it is a plastic clip on our 88 with maybe a spring clip in the end of it. It 'looks' like it should pull off square, but I don't know for sure...

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: N> No clues for getting the linkages off? Should I just pry a bit with a > screwdriver?

Thanks, Mike. I appreciate you digging into it for me.

Clint

So I did my thorough cleaning of the throttle body, and it seems to run smoother and more consistent. Don't know about eating off it, but there's no more black gunk in there. But now immediately after firing it up, it goes up to about 2000 rpm, and sits there.

I tried unplugging the two sensors (one at a time) and then starting it up. When I did that to the IAS, it started like I had my foot on the gas (rapid increase in engine speed). Shut it down, plug in the IAS, then unplug the TPS. Well, that made it run exactly as it did with it plugged in; start and run at 2000 rpm. So I'm thinking the TPS is shot, and I should replace it. Make sense? I had tried adjusting the TPS with no joy as well, even when I went to one extreme to the other. I haven't re-measured the output of the TPS; I'll probably do that later today. But it seems it should be doing something useful.

Clint

So I stopped by the local parts place, and they wanted $280 for the sensor! The manual transmission one was twice as much as the automatic one, and of course, I've got the more expensive of the two.

*sigh* I thought the automatic one had an extra electrical connector on it? So shouldn't it be the more expensive of the two? Ah, well, logic isn't required, I guess.

I checked a "parts recycler", and they had the automatic transmission version in stock, but it was still $75, which seems pretty steep for a used part like that. I think I'll have to find a "pick-your-part" type place. I can yank it out in no time, at least.

Cl> So I did my thorough cleaning of the throttle body, and it seems to run

I checked Advanced Auto Parts online and they get in the vicinity of $75 for a new one - several suppliers to chose from.

Before you go throwing money at it, remove the old one and spray it well with WD40 or contact cleaner. You should be able to get some to filter inside. Get as close to the unit as possible and measure the resistance between all the pins. That !!@#$% thing is a simple rheostat so if you turn it as far as it goes in one direction, you should get several ohms (not sure of the exact value - sorry) between one of the pins and the other two. Leave one end of the ohm meter where it was and turn the thing about half way. Now you should see about half the resistance at one of the pins. Swap thing around to be sure you have contact between all 3 pins at some point. I have been able to clean the wiper arm in a couple of them by soaking the thing in WD40 for a days or so - the shaft is not sealed, so the solvent will seep in - and it sure beats $75!

FYI, AA lists the same part for the 87-90 Comanche, Cherokee, and Wagoneer with the 4.0 engine.