Hard rumbly start followed by weeks of high idle

[bradleyheathhays]

Hey good ppl. The old 96er is having a hissy lately (96 XJ 4.0 with 230k on the spinner). About two months ago she cranked and started normally, but seemed to be idling a little rough. I thought it was my already bad engine mounts just getting a little worse and didn't think much of it. So for the last 2 months, up to 10 days ago, it's only symptom was starting ok but consistently idling rough.

So 10 days ago I changed out my fan clutch chasing down a separate variable engine temp problem (which involved loosening and re-tightening the serpentine belt, don't know if this was a contributing/exacerbating factor, possibly not related at all) and when I go to start again it just cranks and cranks. First crank is 5-10 sec with no engine response. 2nd and 3rd crank the same. 4th crank it gives a half-hearted sputter and quits. After 2 more cranks it barely gets going after some pedal feathering and a prayer. When I step out the ca I smell gas, so I chalk the hard start up to a flooding issue, although no clue what caused it.

Ever since that recent hard start the engine has started relatively ok, with about .5 to 1 second of extra cranking for insurance, but the idle has remained high around 1k for the entire duration when the engine is running until I shut it off. I thought the engine somehow needed to 'relearn' the correct fuel mixture and it would eventually work itself out. I was wrong. 10 days now and the idle stays high no matter what. When I'm driving and let off the gas it just continues to propel itself forward due to the high idle, and I'm having to mash the brake pedal noticeably harder to come to a stop.

Any idea what this is? I'm hoping it's as simple as a MAF sensor or intake cleaning.

I'm all ears. Thanks.

 

[JPNinPA]

There are a few things to check.
1.) For the cranking long try just turning tye key to the on position. Listen for the fuel pump to kick on for 3-5 sec then off. If you dont hear this you may have a pump issue with power or failure. After the 3-5 sec turn the key off and again turn it to on. Wait 2 sec and start.
If this corrects the long start, great. Nothing horrible, but the backflow valve is failing. The above process will keep your cranking low.
2.) A second item to look at is the injectors. A stuck injector will fill the cylinder with gas. The car will not start until there is good enough air fuel mixture. Then idke rough and bad gas milage. To find it place a long screwdriver on the back of the injector and carefully place the handle against your ear. You should here it clicking open and closed. No clicking is the stick one. You could also get a mechanics stethoscope. And do the same.
High idle:
3.) Vacuum leak- being you were tinkering under the hood it is possible to have pulled off, cracked ir damaged a vacuum line. First look around the intake and TB and see that each intank nipple has a hose on it. Follow each hose looking for cracks and that th e opposite side is attached.
Another method is spraying TB cleaner at each vacuum ports and listen for a change in idle.
Lastly is a smoke machine.
4.)IAC- on the throttle body there is a valve that controls idle conditions. It opens and closes as needed to keep the idle at 750 rpms. Over time these get buildup on them and stop working. You could take it off and clean the TB , the IAC opening and IAC. Be sure not to damage the plunger tip.
5.) being this started with an erratic idle you might check the fuel pressure. A failing pump or regulator cant keep the gas flow. This would be noticble at normal speeds. The engine might shudder or slow then catch up.

Always make sure all connections are clean and secure on IAC and TPS. And not to forget the battery.


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