Just replaced the cracked cylinder head and water pump on my 1998 4.0L XJ. Everything cleaned and gone back together fine. Engine temp now ok.
Problem is engine now idles at around 1800-2000 rpm and won't up shift until around 4000 rpm. All throttle linkages appear correct and free. could this be a vac leak etc.any ideas?

 

Sounds like a vacuum leak and a misadjusted throttle valve cable.

 

Probably misadjusted otherwise clean out or replace the IAC and see if there is any change?(Return it if not)

 

Thanks for your tips guys, throttle linkages all OK, vac hoses checked and all OK. Problem must be with the IAC. Will it be necessary totake it to a dealer to reset the ecu or can I just clean or replace the IAC.

 

Have you checked your TPS, Thats whats wrong with mine right now.

 

yeah, tps will cause bad shifting also. Did you actually adj the kickdown cable, or just check to make sure it was hooked up?

 

Did you check intake manifold for leaks? spray carb cleaner (EFI Safe) along the mating surfaces of manifold/Head and throttle body

 

To piggy back on this. If your engine revs up then you know you have a leak. Spray one area at a time.

 

have now removed air intake hose and fired the engine up. with no throttle (butterfly totally closed) and partially blanking idle air duct revs drop to satisfactory. This piont to IAC, as if leaking around gaskets head atc revs would still remain high, does this make sense?

Problem now appears sorted, sticky IAC, now running OK, will fit new one as precautionary measure. Thanks for all the help.