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having issues with engine starting, then rough idle, and lurging during drive

S

steiny

NAXJA Forum User
Location
Fort Collins
any ideas would help. doesn't like to start sometimes, other times it will start. No matter when it starts, it has a rough time settling on an idle about 1200rpm. When it won't start, I can give it throttle and it will usually sputter and fire...again.. rough start. It drives, but if i get the rpms up and lets of the gas very suddenly, it will feel like the clutch was let out too quick, a lurging forward sense. I think it might be fuel pump issue.
any ideas help
thanks
-chris
 
Last edited by a moderator:
need some help with engine problems IDEAS PLEASE

any ideas would help. doesn't like to start sometimes, other times it will start. No matter when it starts, it has a rough time settling on an idle about 1200rpm. When it won't start, I can give it throttle and it will usually sputter and fire...again.. rough start. It drives, but if i get the rpms up and lets of the gas very suddenly, it will feel like the clutch was let out too quick, a lurging forward sense. I think it might be fuel pump issue. It's a '93 XJ, 4.0 L 6 cyl. 5 speed manual. MPI high output engine.
any ideas help
thanks
-steiny
 
Last edited by a moderator:
Re: need some help with engine problems IDEAS PLEASE

Could be any number of things.

First, your idle after 20 minutes of engine/transmission operation (driving) should be between 700-750 RPM. It will be higher when you first start the engine as the PCM increases the idle during warm up.

Now, you may have NUMEROUS things going on here.

What is the state of the tune up? Plugs, wires, cap (brass contacts only), rotor, air filter?

Your TPS, CTS, MAP, MAT, o2 sensor, could be bad and feeding false data to the PCM.

Your throttle body and IAC port may need cleaning. Your IAC could be bad.

You may not have enough fuel pressure. You may not have enough fuel volume. Your fuel filter could be plugged or you have a damaged (restricted) fuel line somewhere.
 
Re: need some help with engine problems IDEAS PLEASE

rpms stay up for hours of of driving. tune up is all good. AEM brute force air filter. I'll try to check the TPS,CTS,MAT, o2 seems to be fine-how do you check o2 sensor other than unplugging it? unplugged MAP sensor and she didn't fire. cleaned the hell out of the throttle body and bought a new IAC and nothing changed about the rough startup.
just changed the fuel filter. I know the fuel pump kicks on but don't know the pressure.
(thanks for replying)
 
just drove it today for about 45 minutes, ran fine when warmed up no lurging when I let of gas petal abruptly, but still had a high idle as usual about 1100 rpms
 
XJ Stryker said:
My vote is CPS

That booger causes all types of issues and it can usually be temp fixed by unplugging and then plugging it back it. May help to spray it out with some canned air sense it is a dust sensitive connection.
Click to expand...

Have you ever seen a CPS cause a high idle?

More likely a vacuum leak. I have seen an MAT cause a high idle and cold engine starting problems on mine. I hear the CTS can cause that problem as well.
 
cruiser54 said:
When CPS fails, no run. Doesn't have my vote.........
Click to expand...

Not true. Guess you have not had the CPS problems I have had.

Granted it did eventually lead to NO Start. But it started out with sputtering.

Uneven RPM

High Start RPM.

Every time I had those problems unplugging and plugging it back it when fix the issue and that worked also for the no start. I finally got tired of doing it and replaced and NONE of the other problem exist or returned.
 
^^^ ECO my jeep would start up and stay at about 1500-1800 RPM and then just hold. That problem didn't return once I replaced the CPS. And yes I had replaced the IAC and cleaned the throttle body numerous times from reading threads on here.
 
It's odd that I've been around these Jeeps since new as a service manager at a Jeep dealership for 13 years, currently own five of them, work on them, and have NEVER seen the CPS cause a high idle.
 
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