I have an 89 xj 4.0 with 160k on it that when you hold the speed steady it seam to miss it doesn't do it if your accelerating or if you let off the gas or if its in park. Also some times when you start it, it doesn't want to idle and tries to die but other time its fine. i have replaced the fuel pump recently fuel filter, pressure regulator, tps, and cps, sea foamed it and cleaned the iac. i checked the fuel pressure and it was good. hoping some of you gurus can help me

 

Sea Foam can kill old injectors. And you sound like the same problem mine had. Run some Lucas Injector/ fuel system cleaner through it and see if that helps, it did for mine for a while, but I know I'll have to replace my injectors..

 

Check the 02 sensor is operating, oh and if your running platinum plugs it will do this also, im having a similar problem whilst mine is cold.

 

What kind of voltage readings are you getting at the IAC? Check also the O2 voltages hot and cold. Your O2 has a heater circuit too so don't get the wires confused when checking voltages.

 

ok i checked t5he o2and this is what i got cold it held steady at .4 after it warmed up one wire was 13v the middle wire went between 1.5 to 3.6 the other wire was .03 . i wasn't sure how to check the iac but all 4 wires were at 13v hope this info help do you think it could be the the o2

 

sorry for the bump wasnt aware of that. just wondering if i should replace the O2 sensor

 

you can never go wrong with replacing a 02 sensor, most replace them when they get a code or are doing a tune up..

As for the bump no problem that's why I let you know..

 

Yeah the O2 sensor is borderline with the voltage. The heater in it is fine and they are what usually burn out first. You should have checked the IAC with the multimeter to see if you have a good ground too.

First - Check ALL of your engine ground connections.
Second - Check the ground wire from your TPS to the firewall to ensure that there is not a poor circuit to ground. If the circuit resistance is high then the voltage reading will be incorrect to the ECU and the computer will not know what the throttle opening is actually at & the engine will not run or shift properly

The ECU uses it's information and commands the unit to extend or retract the pintle, which controls the amount of air which bypasses the throttle plate to maintain idle speeds.

 

If you haven't, remove the IAC and check both it and the bore in the TB that it sits in. Mine was full of... well... tar. After a good cleaning all my hard-start, no-idle, conditions went away. Of course I did cap, plugs, rotor, and wires all at the same time so I can't say 100% for sure if this helped.

Can't hurt.

 

ok i think i have it narrowed down to the IAC because it doesnt move at all anymore with engine hot or cold so im going to buy a new one on friday

 

Take the anglers suggestion and clean everything when you install the new IAC. Let us know if that solved your problems.

 

ok i changed the IAC and it runs nice and smooth thanks for all the help