GQ TD42 Auto rough idle

[jetski657]

Gday,

Have had a search but cant seem to find what i'm after..

Have just picked up a 1991 GQ LWB TD42 auto, it seems to be running fine and has a good service history. The idle speed in N is approx 800rpm according to the dash tacho, when I shift to D and sit stationary with foot on the brake, the revs drop which is normal but the vehicle develops a very harsh vibration. I have adjusted the idle speed and the vibration goes away when it is adjusted so that the engine runs at approx 800rpm when in drive but then when you are in P or N the idle is way to high (approx 1100-1200rpm).

Any clues for me? Was thinking maybe engine mounts or something but all looks OK

Everything standard, no turbo, snorkel, or aftermarket exhaust etc

[threedogs]

Check all Vacuum hoses for leaks or breaks???? flying blind here

[jetski657]

Yea no worries, will be giving it a full service starting tonight and checking valve clearances etc so I'll give all the vac hoses a good going over

[threedogs]

Seems they tend to go brittle and perish over time, only costs about 50cents a metre.
A good going over and service should show up any faults. I'm a big fan Diesel Auto,
not many were made. lucky as sounds like you picked up a goo one. picture would be nice.

[johno90]

No vac lines on td42 :) gq td42 except idle up for a/c. Check your engine mounts etc make sure theres no air in the lines. if all else fails time to start looking at compression, injectors and pump. Also just so you know td42 auto's do have a bit of vibration due to the load vs rpm their under. If you live around brisbane id be happy to show you mine.

[jetski657]

Seems to just be that particular engine speed, gave it a run last night and changed idle speed over approx 400rpm range. Even with Trans in nuetral and no other load on the motor it has a harsh vibration at around 600rpm. Might just increase it slightly to keep engine speed above this when in drive and see how it goes. Checked engine mounts etc and all seems OK. What the best way to ensure no air in the lines? crack fitting at injector to bleed or is there a better way?

[Alitis007]

Have look at your exhaust, it may have been bent some were and its touching the body.