Hello all. I have just changed the Valley gasket on my 2001 4.0L p38. It is now very difficult to get started ( you have to have your foot hard down on the accelerator), runs very roughly, and stalls if you take your foot off the accelerator? Not had much chance to investigate but I assume it’s either ; coil packs not connected up correctly, loose connection or wrongly connected injector plug? Or air leak somewhere? Not sure if I will have the opportunity to look at it tomorrow ( given the weather forecast ). But any pointers greatly appreciated!

well, if it were me, then the quick checks are: HT leads - trace them all from coil to plug, easy to get mixed up. You can get inline lights from Laser tools to look at the HT leads and check they're all firing, although it doesn't really help on sequencing (they flash too fast). Worth checking for fuel pressure on the rail - press the schrader valve with a cloth over it - or even better get a gauge on it - no major reason why the pressure should suddenly not be there if you've hooked things up ok. You can't connect injectors in the wrong sequence (but you could forget to connect one). If MAF is dis/ mis-connected it may do that to you - so worth checking that multi-plug and the IACV one too. Maybe a split in the elephant trunk on the air intake, and worth checking the rubber hoses connecting to the rocker covers too. Do you have nanocom? cd be worth looking at the IACV steps set up, I'm guessing you cleaned out the plenum when you did the valley gasket, although that seems quite tolerant even when the setting's off.
There are other things that might cause your symptoms, but I'm just focusing on what might have been disturbed when you did the valley gasket.

The only thing is to go back over everything you have touched. If you don't remember touching it, you didn't!

My guess would be you have mixed up some of the plug wires . When I changed my coil packs it took my brother and I several trys to get them correct . We found the various diagrams on Google rather confusing. As I'm sure you know, you should not have to touch the gas peddle to get it to start.

Many thanks for the replies. A tad windy to raise the bonnet to the service position at the moment but when it dies down a bit I will get out there and re-check everything I did!

Problem solved! I always find it slightly annoying when a poster does not post the solution when requesting help, so here goes, I went over all the work I had done and it appears that while trying to get the job finished in bad light I got the connectors for the AIC valve and coil pack swapped over. Rather surprised that it still started ( all be it, reluctantly ). Swapped them back over and everything is fine now. Silly mistake but easily sorted out. Many thanks for all the good advice.

Boom! Niiice one.