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VS Ecotec rough idle

primo

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Hi Guys,

This one is a real challange that not even two different qualified mechanics can work out on my 98 seriess II V6 Ute.
I have had a rough idle over the last month that we can't diagnose. It drives beautifully and really smooth, but when coming to a stop it starts to misbehave. Driving off is fine. I have checked all the previous posts (they were really useful) and taken it to various mechanics with no luck and no error codes showing up!. This is what I have done to it over the last couple of months usually with genuine parts-

Replaced Fuel pump & filter, CAS, IAC, temp sensor(tte little one not the larger sender?), Fuel pressure regulator, Oxygen sensors, manifold gaskets.

Removed & cleaned Throttle body, plenum chamber, manifold, injectors where sent away for a proper clean, spark plugs checked, starter motor. Checked the vacum and purge hoses especially the ones connecting to the TB.

The above has certainly improved it's performance and starting but that rough idle is still there!

Would like some further advice on a likely cause. I'm thinking whether a compression test is valid?

One other thing, with the two purge/vacuum hoses that connect to the module towards the back of the intake manifold, how do you know in which order the hoses connect up? ie, there are two connectors, one goes off to the Throttle Body and the other one to the carbon canister, I have the bottom one going to the TB and the top one going to the canister?
 

FstStig

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Have you tried cleaning or replacing your TPS (Throttle Position Sensor)? Cleaning or replacing your MAF (Mass Air Flow sensor)?
 

primo

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no I haven't. The mechanic said he tested the TPS resistance and it was ok. How do you clean the two TPS and MAF? carby cleaner or just wipe any dust with a rag when taking them off as I hear they are delicate things?
 

nathanVY

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I wouldn't think the TPS would contribute to idling issues. MAF possibly though, you can buy maf cleaner, whether it's worth it (or safe) is another question. Wiping it down with a rag can't hurt though.

Join the club with the crappy idle too, mine does it to really bad. Seems to get worse once it's warmed up.
 

FstStig

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Are your engine mounts not stuffed? Just throwing this idea out there but possibly your CAM angle sensor?
 

primo

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replaced the CAS about two months ago. The mechanic "checked" the engine mounts and reckons they look ok.
 

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By CAS do you mean Crank Angle Sensor or Cam Angle sensor, both completely different sensors in different locations.
 

primo

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sorry I meant the crank angle sensor was replaced a while ago
 

FstStig

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ok get him to check the CAM angle sensor.
 

primo

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curious what the CAM angle sensor has to do with idle? I will check it out though.
 
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