mmorris

First off, I'm mechanically "deficient".

I have a rough idle on an 01 Sport and it's throwing a PO301 code. Lately, after delivering senior meals and idling a lot for over an hour (air temperatures here in Missouri are NOT hot!), it doesn't want to start without a lot of cranking and pushing/holding the accelerator to the floor.

I hear no whistling/air sucking noises under the hood. I've sprayed carb cleaner everywhere I can to check for a vacuum leak and the engine RPMs do not seem to change.

First, many posts mention that the rear manifold bolt has a tendency to work loose. The manifold is on the fuel injector side, correct? Can I check the rear bolt tightness without taking much "stuff" off/loose?

Second, I have a Mity Vac for bleeding brakes. Can I use it to check the vacuum system and if so, where and how do I hook it in?

Thanks!

SteveMongr

I don't have a solution for you, just information. When flooring the accelerator during starting, this stops the injectors from spraying fuel which is designed to 'clear flood'.
Here is info on code and previous dealings with this by other members.
http://repairpal.com/OBD-II-Code-P0301
https://www.cherokeeforum.com/f2/cyl...e-p0301-43255/

mmorris

Rear manifold bolt was somewhat loose and I did tighten it using a 9/16" socket with a 4" extension. Made a LITTLE difference but still threw the PO301 code after it was reset.

SteveMongr

Good find on the loose bolt. The manifold bolts torque spec is very low, they are not meant to be tightened like a regular bolt. And they have conical washer that flexes to allow expansion/contraction.
From what I read, i do not see where a leaking exhaust would cause the PO301.
What about the simple stuff first, when was the last time the spark plugs were replaced? Also, your 2001 has coil packs to distribute spark, instead of a distributor. When the coils are failing they can cause the misfire issue.
Here is a bit of info on it. The coil packs can be a common issue.

https://www.cherokeeforum.com/f67/20...-packs-202935/

Also; if the manifold gasket has been leaking for months than it may not seat properly when tightening that bolt, due to carbon build-up or the gasket material being compromised.

mmorris

I can live with the slight, rough idle but the periodically not starting without a lot of "grinding", I cannot. Any suggestions here?

As far as the rough idle:

I have changed out the coil pack and spark plugs, both chemically and manually cleaned the throttle body and IAC, and checked for vacuum leaks with both carb cleaner and propane. I rigged up a grounded metal bar to check for spark at all plugs with new coil: OK.

There is an improvement in the idle, although not enough to stop the PO301 code from reoccurring. My next step is to do a proper vacuum check, a compression check, and a fuel pressure check. Any other culprits? Valve springs?

Thanks.

SteveMongr

Hard to say at this point, but you are on the right track by testing and ruling out.
For others it seems the problem is varied, from CPS, cracked flexplate, no compression, bad valves.
Need an engine guru to assist.
When my 1996 had a rough idle and would sometimes only start by flooring accelerator, it turned out to be corrosion on plug for coolant temperature sensor. That sensor info is sometimes used to regulate injectors. Your 2001 is set up differently.
Idling for extended periods can cause carbon build up, so you may be on to something by suspecting valves.