99 Jeep Cherokee Sport

I've been working on problems with a surging engine, and stalling out so I replaced the idle air control valve, throttle position sensor, and cleaned the throttle body.

Now when I start the car the idle seems better. But with the car in park I depressed the gas enough to get the rpm up to 3 on the guage. When I let off the gas the rpm stayed at 3. I shut off the engine and waited a minute, then restarted. It was hard to start but eventually did. The rpm went right back up to 3 without giving it any gas. So, what might cause this? Might it be the crankshaft position sensor?

Also, after replacing those parts should I have reset the computer in some way? Might the computer be operating with values from before the parts were replaced?
Thanks.

 

Not a bad idea to reset the 'puter, but I doubt that's really the problem. A vacuum leak can cause this. I would start looking for a booboo where you worked. It was not like this before, correct? The simplest explanation is, you touched it, you broke it.

Maybe not, but it's the first place to look.

 

Recheck all those harness connections, and any others you can see. Open them up, dielectric grease while you are in there, make sure they are reconnected securely. If any of the locks on the connectors are broken, use a zip tie to lock it down.

And the vacuum lines/caps too.

 

Sounds like the throttle cable is stuck.

 

I confirmed all the connectors are secure. I went over the vacuum lines and found no problems. I don't have a stuck throttle cable.

I bought a code scanner. It shows check engine codes 505 and 123. But I've already replaced the idle air control valve and throttle position sensor. I also removed and cleaned the throttle body.

The issues still are enging reving, stalling when driving and the car slows down to a stop, some bucking and jerking.

What else should I check?

Thanks.

 

You can have vacuum leaks at several places, not just the vacuum lines. Like, for example:

• IAC gasket
• TPS gasket
• Throttle shaft
• Intake manifold

And you get the picture. Test using ether while the engine is running. And yes, check that throttle cable, just because it's pretty easy to do.