blaze-xj

Hey guys, I have been working on the XJ recently, thanks to CF learning a ton, thanks. I'm have an issue that I think you guys would be good and helping me diagnose.

It's been having a cranking issue for more than a year now, has to turn over several times before it cranks. Recently it started having a very low idle, almost to the point of sounding like it was about to die but never did. I decided to clean the throttle body to try to remedy this. I removed the throttle body cleaned it fairly well, removed the IAC, cleaned it also, put it all back together and put on a new tb gasket, the old one was so brittle it just broke. Since then it does start much quicker, but idles high cold, 800 - 1000k. And it randomly dies when coming to a stop if the engine is cold. It always starts back up though, very quickly as a matter of fact, and runs a little rich at first.

Also when driving on the interstate when it's cold and i let off the gas, it drops in RPM's and speed very quickly, almost like it's being pulled back. This lessens as I drive longer, seems to be gone by the time I'm done with my 15 minute commute to work, RPM's and speed are back to dropping at a gradual coasting pace if I let off the gas.

I've sprayed tb cleaner around the tb while running and no fluctuations in rpm's so i dont think i have a vacuum leak. I may have gotten the map sensor and the tps wet w/ tb cleaner as i didn't take those out while cleaning. I've read many many threads on this, and i feel like it's something w/ one of the sensors, iac, tps or map, and i'm fairly certain all 3 have been blamed in other threads for similar issues.

Any advice or similar experiences and results are appreciated, thanks.

Specs are 2000, Sport, 4.0

Joeymb95

Ok its funny you posted this because my xj just had the same issue since i bought it and its fixed now. Heres what I did:
• installed NGK spark plugs and napa premium wires
• put in a new distrubuter cap
• cleaned the IAC valve and throttle body
• replaced the fuel pump. (Its expensive but thats the root of your problem) the shop told me there wasnt anything wrong with it but they cant tell unless it dies on them. Which mine didnt when i left it there overnight... Twice. But just replace it

And just clean your engine completely. WD40 and a rag makes it shine like new.

Joeymb95

Overall its about a $600 fix but its worth it. So it dosent die on you and it starts/idles like a new car

blaze-xj

thanks for the advice, i actually replaced the spark plugs w/ autolite APP985's about a month ago.

I have a hard time feeling like the fuel pump is the blame because none of this fluctuating idle business started until i cleaned the tb. which actually did help starting, it starts right up, no more holding the ignition open for 3-4 seconds before it starts. i just don't know how long it will stay running. it only shuts off 1-2 times during a drive, once it hits full on operating temp things seem to be ok.

black-knight98xj

Hold the phone for a second. It sounds like you have a pre-2000 XJ, so the rules here are a little different.

In 2000, the 4.0 switched to a distributorless ignition system, so there's no distributor or plug wires. Instead, there's a coil pack and the camshaft positioning sensor sits where the distributor used to be.

OP, it's possible the camshaft or crankshaft positioning sensors could be to blame as well.

Joeymb95

That was the same with mine. Do you prime it(turn the battery on for 10 seconds) before you turn the key over when you start it? If not, try that. If that gets you started faster then its definately the pump

blaze-xj

thanks for the info, I don't believe my 2000 has the camshaft position sensor and i think i've read before that if the Crankshaft Position Sensor is bad it won't start at all.

blaze-xj

No i don't typically prime. after the cleaning the tb it actually fixed the hard starts, but i picked up a new issue w/ the high/fluctuating idle and random stalling.

black-knight98xj

Well, all XJs have a camshaft positioning sensor (with the older distributor-equipped system, the sensor is in the distributor), but since yours is a 2000 it should have just the sensor and a coil pack. The only way it could have the older system is if someone swapped the motor out for an older one and replaced the PCM.

Muaddib420

I would replace your MAP sensor and go from there. $20 part from rockauto.