Cingram

1998 xj, 4.0l. Please help running out of ideas. On warm up get a 60 second of rough miss fire idle, doesn't stall and not putting out codes. Also happens when hot start. I've already done rotor, wires plugs, cleaned iac, new air etc. any help would be appreciated. Trucks only got 145k on it,

JPXJMOAB

How's the fuel pressure look?

bassxj

Map sensor possible

salad

Does it run better if you hit the throttle/gas pedal? What happens after 60 seconds? What is "New air"?

Cingram

New air filter. No, during the 60 second rough idle if I step on the gas it is mis firing for sure. In park or in drive it acts the same. Fuel pressure is something I have been considering but have yet to be able to check. I also do sometimes hear the fuel pump almost gurgling through the gas door.

fb97xj1

If it is the pump 'gurgling', the filter (at the bottom of the tank) may be clogged to the point that it is sucking in just as much air as fuel. Or the pump ingested some dirt somehow big enough to restrict the flow. ???

Those are just guesses, but i dont see what else would make the pump 'gurgle'. Never encountered that one before. But that lack of fuel would cause a rough idle. Need to find out which cylinder has the misfire. Could be the injectors getting dirty.

salad

So what happens after 60 seconds? Does it stall? Does it run fine?

Cingram

Runs great after the 60 second rough idle. Yea I'm thinking about changing the fuel pump out seeing how this year does not have a in line filter

salad

Ok, that's very important information. If you just turn the key to START, OFF, START,do that say six times, and start it again. Does it still run rough?

This happens when the engine is cold, too, right?

Cingram

Tested fuel pressure, solid 50psi while running. It does do this occasionally on cold start as well while warming up , again only for about 3 minutes. Just did a coolant temp sensor and so far so good. But it's only been a day or so....

97grand4.0

Need to do the bleed down test too. Should hold pressure at least 25lbs after a certain amount of time, not sure, think is 5 minutes. If it plummets when you shut it off, regulator/filter is bad.
CTS was a good guess, I would also think time for a new iac. junk yard iac to sub in are a good inexpensive way to check. Nothing beats the obd2 scan tool to watch tps volts, cts temp, and map. But I would do the bleed down first. just my 2c.

Cingram

Just to follow up. Replaced the coolant temp sensor. While doing so I noticed I had a loose ground wire to the fire wall. Not sure which one was the issue or both possibly but either way the xj is running top