No/rough idle

[P38]

Working on my son's 2003 Disco 2 4.6 BOSCH engine having fixed a bunch of leaks, pumps etc. I cannot understand why it won't idle under 1000. It fires up fine, revs well past 1000 but just doesn't want to idle. Any ideas? I didn't have this issue with my 2002 4.6 P38. It's got me stumped. Everything appears to be plugged in correctly, plus wires etc.

Your ideas appreciated.

 

[discostew]

Make sure the throttle is settled on the stop screw. If you removed the 2 bolts that hold the throttle cable bracket on the front of the plenum loosen them and see if the throttle will settle onto the stop. Then snug them back up.

 

[boxster]

Maybe stepper/IAC valve dirty or faiiing.

 

[best4x4]

Yep check TB and CC cable adjustment for sure.

 

[Flyfish]

Check for vacuum leaks; loose hoses, hose clamps etc.

 

[P38]

Make sure the throttle is settled on the stop screw. If you removed the 2 bolts that hold the throttle cable bracket on the front of the plenum loosen them and see if the throttle will settle onto the stop. Then snug them back up.

I dis-assembled the bracket without touching the adjustment screws, so this shouldn't be a problem, but I'll recheck position. Thanks!

 

[Flyfish]

I dis-assembled the bracket without touching the adjustment screws, so this shouldn't be a problem, but I'll recheck position. Thanks!

It may be helpful to know what all you took apart, what things you fixed. Just to identify possible vacuum leak spots.

 

[discostew]

I dis-assembled the bracket without touching the adjustment screws, so this shouldn't be a problem, but I'll recheck position. Thanks!

No it can be the problem for sure. That bracket will move enough to cause the throttle to be off the stop. I only take the two bolts out as well and always check to make sure the throttle is on the stop screw before. I torque them.

 

[Swedjen2]

How old is the stepper/IAC valve? Rough idle is one of the symptoms.

 

[discostew]

How old is the stepper/IAC valve? Rough idle is one of the symptoms.

I know it seems logical but I really don’t recall seeing one fix anything. Plus if I’m reading all this correctly it was idling fine before he took it apart. So that makes it even more of a stretch

 

[P38]

It may be helpful to know what all you took apart, what things you fixed. Just to identify possible vacuum leak spots.

I pulled everything off to get to and replace the valley gasket, valve cover gaskets, front cover, replace all water hoses.

 

[JUKE179r]

Got any trouble codes?
Is the throttle position sensor plugged in?

 

[Flyfish]

I pulled everything off to get to and replace the valley gasket, valve cover gaskets, front cover, replace all water hoses.

Very possible there is a vacuum leak. Try to do a smoke test and check.

 

[P38]

Thanks, everyone. I believe I have tracked the culprit down. Will be testing my theory at the weekend when the temps get back into the mid 30s!

 

[Flyfish]

Thanks, everyone. I believe I have tracked the culprit down. Will be testing my theory at the weekend when the temps get back into the mid 30s!

What’s the suspect?

 

[P38]

I rechecked all the connections and hose clamps, thinking a vacuum leak or similar, but no dice. I'll talk to Will T about a replacement air idle and swap it out. At this point, I am happy to swap out some potential problem parts - I have 3 BOSCH engine Rovahs to maintain, so it's NBD to have some known good parts kicking around.

 

[best4x4]

Spray the IAC with carb spray and shake it. It will usually break free and keep spraying it until it rotates freely. I have yet to swap one out I couldn't save from cleaning on a Bosch/Thor setup.

 

[discostew]

I rechecked all the connections and hose clamps, thinking a vacuum leak or similar, but no dice. I'll talk to Will T about a replacement air idle and swap it out. At this point, I am happy to swap out some potential problem parts - I have 3 BOSCH engine Rovahs to maintain, so it's NBD to have some known good parts kicking around.

Yep, I agree totally. You took it off and set it on the bench and it failed.

 

[rovercanus]

Are your fuel injectors seated properly?

 

[P38]

Well, it seems that I didn't torque the intake manifold bolts sufficiently. Go figure. So it created a vacuum leak - as well as a sight coolant leak but I didn't notice that.