my 88' hunts (750-500 rpm's) only when first started, why?

88' 4.0 renix, 5 spd.

i get crappy millage (work is about a mile one way) and in the morning when i start it up (or when the motor is cold) it turns over ...goes right to 750 rpms for a min or so...then starts hunting up and down almost stalling to 750 rpm's.

it never "high idles" when cold...right to 750...then hunts...when it warms up its fine...stays at 750.

does not miss at all...plenty o power...just the initisal hunting...i would like to get this solved soon.

can i get a point in the right direction please...what to test?

128,000 miles...and i don't drive it everyday...this is "my beater" so to speak...i paid $100 for it and put in a clutch...i drive my 02 maxima most of the time.

thanks

Good deal for $100!

My '88 did the same thing until I cleaned the throttle body. Just remember to remove the sensors prior to cleaning. Search "throttle body cleaning" and you should get a bunch of info, it's been covered here quite a bit. Also, I have heard that poor grounding can cause idle problems I would check these too. The wiring on the early XJ's used for grounds and the charging system is problematic and a lot of problems can be prevented when upgraded. Good Luck

Woody

well...i cleaned the shit out of hte t.b. when i first got it....but left the sensor (tps?) in there...so i am wondering if i screwed it up whn i cleaned it....i don't remember it doing it before i cleaned the t.b.

the grounding could be a prob too...i tried jumping a car the other day and no go....then another car pulled up and jumped it just fine (xj was running)

i might have a vacume leak too...but i only hear it in 4wd

Check the intake manifold for air leaks. The MJ I had a bit ago did the same thing, the idle would go up and down for no reason but it ran great on the hwy etc. I eventually found most of the intake nuts loose.

bump...any other input...bad o2? (do they need to warm up?)

Make sure the plastic line from the MAP sensor to TB is pushed into the TB grommet all the way. Might be a poor fit until some heat starts to build.

Could be a temp sensor or IAC. The TPS also has some effect on IAC position, check that too.

is there a way to test the temp sensor (the gauge works fine) and the iac/tbs?

thanks

My '88 also hunts when first started. Just for a few minutes then it evens out. When I first bought it the rpm's would race real high right after starting then it would come back down. After cleaning the throttle body it stopped racing but it still hunts for a few minutes before smoothing out. The engine will even die sometimes.

As far as testing of sensors goes, most of them can be tested easily. Here is a great source:

http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm

If you solve the hunting symptom be sure to post it because its bugging the crap out of me

John.