Riley Thomas Greiner

Recently bought an 88' Cherokee XJ with a 4.0. When I went to go see it wouldn't start. But after unplugging and re connecting the CPS it ran but really roughly. Idles low at around 200-300 rpms. Replaced the tps, cleaned throttle body and IAC, replaced O2. Also have a MAP sensor just installed as well. Replaced the dreaded CPS and still no major improvement. The valvle cover gasket looks like it needs to be replaced. Repaired replaced some vacuum lines that needed it but haven't found to many issues with that. When I rev it up then let off the gas it usually kills it but will start back up and continue to idle roughly. Also replaced fuel filter. The TPS has been properly adjusted to 17 percent of the base reading from the multi meter. Any ideas on would be greatly appreciated. I've done a lot of research but so far efforts have not seen any real results. Just looked at the C101 connector and it was terribly tarred and nasty on the inside. Is that a possible cause for it to idle poorly? Haven't got to cleaning t yet as I'm out of cleaner at the moment. Any input would greatly be appreciated!

dcollins3208

Could be one of several things really.

Check the entire ignition system.
Check for frayed or broken wiring on the fuel injectors.
Could also be a weak fp so check the fuel pressure if you can

'90Cherokee

The C101 is crucial for engine management. The best fix is to eliminate it. Search for Cruisers tips, he is the Renix master and outlines testing and repairing all the Renix stuff very well.

cruiser54

Test for fuel pressure next. Should be 31 PSI at idle with the vacuum hose connected to the fuel pressure regulator and then jump to 39 PSI when disconnected.

As suggested, click on the link in my signature below and complete Tips 1 through 5.

cruiser54

This one

Riley Thomas Greiner

Thanks for the replies. I looked at the vacuum for the MAP but it looks surpringly in good shape, just seems to me like all the connections and plug ins are loose if anything, could that affect it?

cruiser54

YES.

Riley Thomas Greiner

Test fuel pressure from the rail, was at 21 when I pulled the vacuum and with the vacuum on. Another possible problem perhaps?

cruiser54

NO!!!!!!!! Should be 31 with the line on and 39 without it on!!!!

Riley Thomas Greiner

For the MAP vacuum, should there be any rubber hose on it or just the thin plastic one? Cause it has both running from the TB to the MAP sensor

cruiser54

What about the fuel pressure issue?

Riley Thomas Greiner

That could explain the poor fuel pressure reading, I looked up that vacuum line to the map and it should be one piece, not three like mine. PO must have snapped it and thrown that small rubber hose on there as a quick fix. Will check back when replaced with proper line.

cruiser54

Don't get your hopes up that fixing that line properly is gonna increase your fuel pressure. You'll just have another fixed and behind you.

ehall

The first hash mark on the tachometer is 500 RPM. I'm not sure its possible to even run at 200 RPMs. Normal idle is 750ish. My knee jerk reaction would be to suspect the IAC. Low fuel pressure would also explain the problem.

Riley Thomas Greiner

Fuel pressure was at 21 PSI when I hooked it up to a fuel pressure gauge, just did a homemade fix on the MAP with no real improvment on idle. Could the MAP affect the fuel pressure?