87 Renix-hard to start when warm

[Cal-XJ]

My xj starts ok when cold, but after it gets warm it takes alot of cranking to get it to start. It turns over just fine but sputters and bucks something awful. Then when it does start it revs up to about 2k for 1/2 a minute or so (sometimes even longer)
It has a new (1 yr old) fuel pump, fuel filter, and vacuum hoses.The cps has been replaced a few years ago.
I've cleaned the airfilter, and IAC, checked fuel pressure. The only thing left according to the Haynes manual (no FSM yet) is a bad engine ground or the pick up coil in the distributor. Is the pick up coil the same thing as the Sync sensor talked about in this thread by 5-90?
http://www.naxja.org/forum/showthread.php?t=86077&highlight=starting+problems
Is it also called a stator? How does one check it?
BTW, I love this site. You guys Rock!

[jeepdude10000]

the sync sensor is actually camshaft sensor, and it is in the dist.
hve u had this problem long?

[Cal-XJ]

yes, about a year. it seems like its been getting progressively worse. At first it just did it on hot days during the summer or when I had driven it on the freeway 20 or 30 miles. After a while it seemed liked it didn't have to be as hot out for it to happen or for me to drive as far.

[jeepdude10000]

have u checked ur temp sensor?

[Cal-XJ]

No I haven't. I assume you're talking about the one on the block, right? I like your signature. I take it you've been married!

[jeepdude10000]

the one near the back of the block on drivers side, tells CPU what temp it is, different then the one gor gauge.

And acually never been married, close though, just dont know if its worth it. Hear it on some show, dont remember witch one.

[96XJay]

Did you ever figure out what it was? My 88 MJ suffers from the same exact problem.

[Bender]

I had a similar problem with mine a couple years back but it was fairly intermittent...it wouldn't always occur when the vehicle was warm but often enough it was a pain.

Turns out it was my ignition coil module. I had some spare parts so I started swapping things over to see what was causing the problem. When I threw in my spare coil and module the problem never came back.

[96XJay]

Thanks for the suggestion. I'll definately look into that. Anyone else have a similar situation occur?

[Ecomike]

Look up "high idle", and "Intake Air Temperature" sensor (IAC) do not search the three letter accronyms, the search tool here requires a minimum 4 letters.

The IAC, in the intake manifold, the coolant temperature sensor (CTS) in the block are the most likely suspects based on the temperature sensitivity of the starting problem, followed by the high idle. You can test them with an Ohm (resistance) meter, multimeter. They are simple temerature sensitive resistors.

Less likely but possible, is a lose, dirty variable ground (there are 2 on the block and 2 on the fire wall plus the battery ground). Also, the TPS, and a heat activated or triggered vacuum leak somewhere. Also a heat activated igniton wire leak to ground could cause this. Even a CPS that does not like heat is a possibilty.

[Shorty]

another thing to check (cuz there aren't enough already) is a sticking EGR valve or solenoid- if they open the valve during a trip but fail to let it close when it should, it would be starting and running with an unregulated vacuum leak (through the exhaust) and can be a real PITA to locate.

next time before you start it cold, remove and PLUG the vacuum line TO the EGR solenoid (intake manifold side of solenoid) and run it a while. If if restarts better this way, you've got an EGR valve sticking open until it cools and shuts.

this is not the most likely cause, but it's easy to check and often overlooked!

--Shorty