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[Milton]

New (to me) 95k miles V6 2.5. V cheap due to problems dealer couldn't/wouldn't fix.  All done now, or easily doable, except this puzzler.

The engine idles poorly when warm. Ok for 5-30 secs, then stumbles and revs back to idle.  Does not stall.  (Air Con is OFF)
Runs v smoothly when driven grandpa style.  Begins to hesitate and fails to deliver power if throttle used more heavily. Will revert to smooth after a couple of minutes more grandpa driving.

Engine bay pretty clean. No smoke or steam. Oil and water fine.  No undue hissing when running. No obvious cracked tubes etc. Tappets mildly noisy.  Temp indicator hovers around 80-90 mark, never red. 

Paperclip test shows code #135  ("Telltale (Checklight) Voltage Low"). All instruments work fine, but I have seen a Brake Light warning, and the Level warning is on (needs linkage fix I believe).  I suspect the #135 is not relevant to the engine issue.

I've read a fair bit about MAF sensors, lambda, ICV etc, but I'd like to know if anyone has a specific idea about these type of symptoms before I get elbows deep into a new (to me) engine bay.

Many thanks.

[mickyboy123]

im no expert but could it poss be a crank sensor, im sure its common on those. some 1 will probly confirm shortly

[05omegav6]

Check light tell tale is the EML... probably a missing bulb...

Clean the idle control valve for starters... also, does it idle any better with the MAF sensor unplugged

Doesn't sound like crank sensor symptoms as don't include stalling/failing to start

If the idle control valve is gunged up, the throttle body might benefit from a good clean too...

[Milton]

Thanks for the suggestions. I'll start with the MAF as that's an easy one, then work my way through the list.  I may ask for more ideas as/when I make discoveries, and will post with a solution anyway, when fixed.  There, that's confidence for you!

Cheers, M.

[chrisgixer]

Possibly ignition system. Any oil in plug wells?

[Temetsy]

Possibly ignition system. Any oil in plug wells?

I'd say its an ignition issue too. Too weak spark to fire on full throtle/rich mixture after cold start.

E: oh, rough idle when hot.. My bad

[TheBoy]

Do NOT change the MAF until proven. 2.5/3.0 MAFs generally either work or don't, rather than misread.

If its missing/hestitant under load, but with no codes, firstly visually check over the entire HT side. If that's OK, it needs some live data read on it.

[Andy H]

I wasted a lot of time trying to fix a misfire on my 1994 2.5 V6.

Eventually I changed the spark plugs - problem solved

The moral of this tale is: do the basic maintenance before looking for a complex/expensive problem to fix.

Basics include
- spark plugs
- fuel filter
- air filter
- cam belt

[cem_devecioglu]

Milton, you will need to check a long list including ignition components, crank sensor etc..


imo, find a good working omega , with a helpful owner and try some ignition parts from his car..


dont skip air leaks or assume there is no, the six gaskets under plenum can easily leak when they are old or hardened..


and I'm suspicious about your crank sensor which will take some time to test/route 


if you try those on a purchasing base you may need a thick wallet I'm afraid..

[tigers_gonads]

Sounds like HT / Spark to me
Plugs, leads, coilpack in that order