2000 XJ Stroker, CPS causing Eccessivly High Idle?

Hi everyone. I've been stalking the forums for a few years now and this is the first time I've ever posted.

I had the notorious 0331 head problem on my 2000 XJ and decided to go the stroker route. So we finally got the brand new 4.7L in and after the first start immediately noticed an extremely high idle (I cut off the ignition before it hit 3000rpm).

We checked for vacuum leaks and couldn't find anything wrong. We think we narrowed it down to the camshaft position sensor being far out-of sync. When we originally took the CPS out of the old engine we didn't know to make sure we had TDS and use a pin to hold the CPS in place. Looking it up in my haynes manual it states that you have to use a scan tool to adjust the CPS. Does anyone know any tricks that doesn't require us trailering it to the local Jeep dealer? Thanks in advance.

all i have to say is strupid distributorless ignition....

rbishop said:

We checked for vacuum leaks and couldn't find anything wrong.

Click to expand...

Are you sure you don't have an air leak from the gasket between the intake manifold and the head? That is exactly the sort of thing that can cause a very high idle.

I was going to say the same thing .. this post screams intake leak.

We checked the intake (and gasket) connections a few times. All the bolts are tight and are seated well. If it was a vacuum issue wouldn't it have to be pretty large leak (ie: easy to identify) to immediately rev to 3000?

In any regard, I've been searching the forums and think I may have found the cause of the problem. A faulty/dirty TPS or IAC. My brother cleaned up the throttle body/intake and may have damaged a sensor in the process. The CPS shouldn't even be able to increase the idle, should it?

Can I diagnose the IAC/TPS by unplugging them and starting it up? Or is that risking damage?

rbishop said:

We checked the intake (and gasket) connections a few times. All the bolts are tight and are seated well. If it was a vacuum issue wouldn't it have to be pretty large leak (ie: easy to identify) to immediately rev to 3000?

Click to expand...

No, not really. Let the engine idle, and spray wd40 around the intake gasket the whole way around while its idling. If the idle rises or drops when you hit a specific area, theres a leak there. It does happen.

Well we unplugged the TPS and IAC and it still idled extremely high.

Trouble is it's racing past 4000 RPM and doesn't seem to be slowing down. We're forced to cut the ignition and don't have time to spray the gasket down by the time it hits 4000+. On the plus side I have a different style gasket that we're putting on now. It looks like this new gasket will seal better. In the mean time I'm going over the intake keeping a close eye for any cracks, etc..

I'm keeping my fingers crossed.

rbishop said:

I'm keeping my fingers crossed.

Click to expand...

Keep us posted.

I had the same problem when I swapped a 4.0 head and injection into my old YJ. It drove me nuts until I realized there is an idle stop screw. It's about impossible to adjust with the throttle body in place. I yanked the throttle body, removed the screw from the bottom and put it in from the top to make it easy to adjust.

Turns out it was a vacuum leak. The gasket was seated improperly on the head. We just took the intake off, pressed around the gasket, made sure it was seated as tight as possible all around (especially around the guide points), bolted the intake back on and sure enough, smooth idle.

After a few weeks of headaches the stroker is finally in, the header downpipe is fabricated and in, and everything's running fine. Thanks , you guys came in handy more times than you'll ever know..

cal said:

I was going to say the same thing .. this post screams intake leak.

Click to expand...

Seems I beat you to the right answer again.