88 4.0 High idle.... again
 

First off I want to say thank you to everyone who has helped me with my Jeep thus far. It is running better than ever.

I have been researching ways to improve my MPG and done the following in the past six months. New IAC, MAP, and TBS, sensors, ( o2 was about two years ago) also sprak plugs, wires, disributer cap and rotor, new Spectra cold air intake and Dyno MAx exauast.

The plugs were kind of a chocolate brown when I replaced them. The engine idles at 500 rmp when cold but then it idles at 1500 rmp when runing for 5 minutes. Also the temptrature gauge never gets past the first quarter mark ( I know it works becasue it does gradualy go up once the vehicle is runnig.)

Any ideas on what I might try to do next?

Also about a year ago I put in all new injectors and I cleaned out the throttle body until it was all shinny.

Sounds like a vacuum leak once warm. I use wd-40 and spray around seal areas and listen for a change in idle. Check all intake maifold bolts when cold, starting in the middle and working your way out, you might find the ones close to the firewall loose...i did.

How old is your thermostat?

The only thermostat to use is the factory one. $23.35 at the dealer. And yes, the low temp will cause fuel mileage reduction.

Did you adjust the TPS on the engine side after replacing it?

I checked the intake bolts and all of them were tight. I have to confese that I had a shop replace the TPS so I am not sure if they did. They told me that they would adjust the new one once it was in so I think they did. They work a lot on Jeeps.

I thought the low temp. might come into play but whenever it gets hotter than the first quarter it runs really rough. It only gets hot when its hot outside and it sits, like at a drive through, or when I am backing in my boat and it sits for a few minutes at the steep incline. I will check for any vacum leeks. It seems to be geting worse the more I drive it. So I am hoping to nail this down. Thanks again for all the feed back.

I would do the stat just cuz.

And I would do a complete ground refreshing, sensor ground test, C101 cleaning, and connector refreshing. Click on the link in my signature and check out #1, #2, #3 and #5.

I will start cleaning and let you know how it goes. Thanks for your help.