fitrider82

Hi all, appreciate all of the help you can provide, I’ve done as much reading as I can and wanted to avoid making what seems to be a repetitive post but I’m stumped.

‘93, 4.0, AW4

Parts replaced:
I recently replaced valve seals, had the head resurfaced, head gasket, rear main, oil pan gasket, valve cover gasket, new injectors, pigtails, replaced all vac lines, bored throttle body, big cable upgrade, swapped to ‘99 intake manifold, new header and NTK O2 sensor.

Problem:
The Jeep has been sitting for about 2 years as i slowly did everything above, I started her up successfully last week and have a high steady idle of ~1700 RPM. When I blipped the throttle I’d get a small hesitation. The idle is very smooth with no fluctuation.

Troubleshooting:

Picked up an O’Reilly’s TPS for it, as we broke the stock one when taking everything apart, read the forums, people said these can be bad out of the box so return/replaced the first one and tried a second one (I know there are chances another one can still be the cause so I ordered a Mopar TPS and will return the O’Reilly TPS when it gets here). The second TPS resolved the hesitation when blipping the throttle, it is perfectly responsive now but still idles high (Mopar will be here next week).

Tested the voltage by back probing the center pin of the TPS, shows ~.72v at idle and at WOT ~3.4v (numbers off the top of my head as I’m posting this, not sure if I did this test procedure right, I found the big write up on multiple forums but it’s not specific in which pin to use, and people mention immediately seeing 5v, this confused me as I’m not good with electrical).

I took the IAC apart, cleaned it AGAIN, the IAC is completely locked up and will not telescope in and out by hand, is this normal?

Did a smoke test with cigar smoke, could see a little smoke coming out from around the TB.

Did a vacuum test to the manifold, 17hg steady.

Sprayed carb cleaner while idling to detect leaks, found if I heavily soak the rear of the intake manifold the idle dips to a normal level so it seems I have a vacuum leak? Wouldn’t the vac test that I did previously make this evident?

I’m running in circles and about to take it all apart to retorque the manifold/header bolts. Please save me from going through the trouble if I’m overlooking something.

-Mike

fb97xj1

The new header is probably hung up slightly on the alignment dowels. It happens quite a bit. That alone can cause a high idle as it sucks in too much air. Its a huge vacuum leak.

Never operate the IAC by hand. Inside is a little motor that is electronically operated by the PCM.

Is the TB leaking between the TB and intake? Did you use a gasket? Or from the throttle shaft?

fitrider82

dup reply.

fitrider82

I was hoping I wouldn't get that answer, not looking forward to fooling with the header/intake again. Is it feasible that I'd receive a steady 17hg reading on a vacuum gauge even with a leak?

The IAC has a metal sleeve around it, are you referring to moving a motor inside of that? There is nothing on my IAC that actually moves externally, is this normal? Could it be seized from sitting for 2 years? I made sure the o-ring is installed on the IAC to help vacuum at the IAC/TB mating surface.

The TB is leaking (from what I can tell with a small amount of smoke coming out of it) around the throttle shaft, I used a gasket at the intake mating surface.

Thanks for the reply fb.

cruiser54

Throttle body.... Butterfly closing?

fitrider82

butteryfly closes completely and actuates smoothly, doesn't get hung up at all. I'm afraid it's a vac leak at the manifold but still don't understand why my vac reading was steady at 17hg if that's the case. Mopar TPS will be here today.

Cummins93

To test your iac take the intake hose off the throttle body. While idling occlude the bypass port with something that can't get sucked in ( I use my thumb). Gradually occlude the port until the engine rpm starts to drop and struggle. Hold it there without stalling the engine for about 5-10 seconds. Then take your thumb off the port. Your rpm should raise to about 1500 then within about 10sec return to normal idle.

If you have a vac leak it will become more pronounced while choking the engine. If the idle does not drop with the bypass port completely covered you have a vac leak.