89 XJ Rough Idle help

I have searched the forums, but see a lot of acronyms I don't know. My jeep starts every time, but cranks for about 2 seconds before it fires up. It has never stalled, but has gotten close (enough to dim lights for a moment). It also shakes the whole jeep like a diesel (In park and drive). The jeep has sat for the last 2 years, and so far has these new parts.

Oil + Filter
Air Filter
Fuel Filter
Coolant
Water Pump
Alternator
Battery
Plugs (NGK)
Wires and Cap
Belt
Thermostat and Housing
Harmonic Balancer

I am on my 3rd tank and run lucas fuel injector cleaner. I got 17 mpg on the first tank (1/2 tank of 2 year old fuel). 16 mpg on the second tank (T-Shooting heat issue, so was idling a lot). I seems to run pretty good while on the throttle, it won't break the tires loose. It idles at around the first hash mark on the rpm gauge. Also, the jeep has 133,000 miles on it.

did you make sure that the gaps on the plugs were correct? most cases new plugs aren't gapped to the proper spec straight out of the box.(common misconception) other than that make sure you don't have any vacuum leaks anywhere. sounds like that may be where your problems lie.
also there is the possibility that the fuel injectors need a good pressurized cleaning.
just my $.02

I did gap the plugs to what it said in the manual, .35 I believe

It could be a vacuum leak. I'd look there first. My 88 was running exactly like you describe when I bought it. It idled low, and the whole truck would shake at stoplights. If I had the hood open, I could watch the light dim as it almost stalled. I got mine running much better with a little bit of work. First, I took the throttle body out. I cleaned it really well with Gumout to remove all the carbon inside. While I had it out, I pulled out the IAC and made sure the seat and passages for it were clean. Finally, I adjusted the TPS. It's still not perfect, but it's pretty close and I do think there is a vacuum leak because I have no vac at my cruise solenoid.

I don't know what the IAC and TPS are. Someone said the 2 vacuum lines on top of the valve cover could cause it. I thought one of them was a pcv valve. I did see something below the throttle, it is hard lined to the throttle and has a cable going to it that is really loose. What is that for and should the cable be tighter? I was going to take everything apart this weekend and clean it. How do you check for vacuum leaks? I am new to this vacuum stuff.

Shane01638 said:

I don't know what the IAC and TPS are. Someone said the 2 vacuum lines on top of the valve cover could cause it. I thought one of them was a pcv valve. I did see something below the throttle, it is hard lined to the throttle and has a cable going to it that is really loose. What is that for and should the cable be tighter? I was going to take everything apart this weekend and clean it. How do you check for vacuum leaks? I am new to this vacuum stuff.

Click to expand...

IAC - Idle air control motor. This can be removed and cleaned (sometimes helps).

TPS - Throttle position sensor. Can be adjusted. Not sure what the exact figure is but it should have a certain output voltage at idle. A service manual (Chiltons, Haynes, factory, etc.) should tell you how to adjust and what to adjust it to.

To check for vacuum leaks, I've had success using a NON FLAMMABLE brake parts cleaner and spraying all of the vacuum lines and intake manifold (especially the areas with gaskets) with it. If the idle changes, wherever you're spraying is where the leak is.

Before you start pulling too much apart and get in over your head, you might save yourself some time and aggrivation and possibly save yourself from making the problem worse by getting a professional to diagnose it for you.

Well I cleaned the throttle body all nice and shiny with deep creep, I also cleaned the IAT probe and other bits around that area. I adjusted the TPS but couldn't get it into spec. Chiltons and pics online show a different TPS. They said to use the 4 pin connector on the TPS, but the connector is like a 20 pin. There is a 4 pin that comes off that with only 3 wires going into it (A, B, and D). I got 4.56 steady between B and D, and A and D would change with the throttle position and when you rotate the TPS. I couldn't get it into spec so maybe it's bad. When the key is in the run position by the way. By spec it said to divide the 4.56 reading by the pin A and D reading and it's supposed to be like .8 something. Anyway, it idles higher now like 900 to 1000 which is too high I think, but it doesn't nearly die at idle anymore.

I also did the seafoam through the throttle body procedure which made it much smoother. I don't think I would hear the thing run If I had a tailpipe and muffler. I still sounds like it has an occasional miss at idle. I think I might just take it to a shop that mainly works on Jeeps and see what they can find.