Common Problem Sputtering.

92 xj, new 4.0....

have this weird sputtering problem. Its present at idle and coasting, not under throttle or decel. It sounds like a sputtering from the engine but if I punch it its gone. I have replaced many things since putting the new engine in.
New wires, plug, cap, rotor, TPS, +/- battey cables, Ignition switch, fuel pump, fp relays, asd relays, fuel filter, o2 sensor, air filter, disty and the problem is still there. I suspected cat but wouldnt it sputter under hesitation?

Tommorrow I am going to look for exhaust/intake/vaccuum leaks and do a fuel pressure test. I am starting to think the regualtor is bad or there is an vaccum leak somewhere, hell maybe the injectors are shot, though still gets good gas mileage.....any help would be appreciated....

Check and clean the IAC- Idle air control valve- before you too excited checking stuff.

I actually took the thottle body off and cleaned it, the IAC had smutcz all over it. Didnt do much.....I have unplugged the IAC and got no change in idle quality..... Is the sputtering is at idle and coasting the IAC would make sense.....HAve any suggestions on how to test it...

Should there be an idle change when I remove the vacuum hose from the regulator? Imean I pull the hose and can feel vacuum on the hose end, I block the hose end and no change in idle.....

I clened the IAC again, is there anyway to test it? Haynes doesnt say much.

you need to have a stepper motor exerciser. You can't just put 12V to it and see if it jumps, I believe it's controlled by a PCM setup from the ECU. Have a dealer check it or just replace it. IIRC i remember reading about a holley generic part that was interchangeable and it was a bunch cheaper, somewhere around $30. You'll have to search to get the P/N.

You might be able to take the airtube off- start the vehicle *!be careful there is alot of vacuum at the throttle body!* Shine a light in the little nook where the IAC is and see if you can see it move at idle and with spraying a little carb cleaner in there. I don't remember if you can see it or not.

*Question- Did you happen to bump or push in the plunger when you cleaned the IAC either time?, If you did then the IAC is junk.

Had similar problem with my 88 xj. Did the same thing changed everything and the kitchen sink just to find that there is a sensor on the rear of the engine which cause the problem. Found this by looking at old service bulletin.
Had shop replace it and bye bye problem

BingBing said:

You might be able to take the airtube off- start the vehicle *!be careful there is alot of vacuum at the throttle body!* Shine a light in the little nook where the IAC is and see if you can see it move at idle and with spraying a little carb cleaner in there. I don't remember if you can see it or not.

*Question- Did you happen to bump or push in the plunger when you cleaned the IAC either time?, If you did then the IAC is junk.

Click to expand...

The plunger, I did move it around, but never changed the problem. The thing is pretty squeeky clean, I think its toast, 300k miles, cant complain about that.
I will jsut replace it, I am interested in this holley part number, will search for that, thanks for the heads up/