Idle speed & "hunting" rpm when coasting

[bushman67]

Two fold question: (4.0L)

1) Ideal idle speed. 800 is norm right? I can't get mine down below 1200~1250. I soaked the TB in cleaner, taken it all apart (was pretty nasty), cleaned AIC (but not replaced). Also, couldn't find any vac leaks (in hoses at least). Idle is consistent, doesn't vary at all. The odd time, I've seen it drop to 1000 at a stop. At this speed, the tranny is pushing enough, I put it in neutral when at stop lights. -- Time for a new AIC maybe?

2) In drive, coasting off gas at highway speeds the engine 'hunts' -- kicking between 1250 & 1750. Transmission flush & filter?

Any suggestions?

[jpthing]

This is on the 96 xj?

[tubby]

Just had a similar problem with my idle. Climbed to 2000 RPM and settled to 1300. I cleaned the IAC  to no avail. It was my TPS.

1. My idle is back to it's normal 900 RPM

2. The XJ would also "hunt", "bog down", " hesitate" at highway speeds

Ten minutes of changing out the TPS and everything is back in order.

HTH.

[bushman67]

Yah, the 96.  I'll see if I can score an entire new TB first, if not I'll start with the TPS instead.

Any other ideas?

[jpthing]

I would likely try the tps too. Of course using sensors as a diagnostic tool can be costly and foolish, but a tps is a good thing to have a spare of anyway. you could also test the tps using the procedure in the haynes manual but I would go try to find a scrapper tps or two.

good luck!!

[tubby]

I would likely try the tps too. Of course using sensors as a diagnostic tool can be costly and foolish, but a tps is a good thing to have a spare of anyway. you could also test the tps using the procedure in the haynes manual but I would go try to find a scrapper tps or two.

good luck!!

Ayup! TPS's are usually in the $50 -$60 price range. I found it cheaper to go to PNP and snag a few for spares. There's a good chance that you will need to change a few over the years if you own an XJ.