25 replies to this topic

[Horace]

Hi,

 

Got a VXT with 98k miles.

 

After about an hours driving today, I was travelling along in traffic at about 50mph about 2k revs.

 

The car seemed to slightly drop power as though there was a restriction in the fuel flow, then it came back fine, then slight drop again.

 

It did this on a number of occasions, and gave me that sinking feeling (here we go again with the breakdown).

 

I was constant on the throttle throughout, and the car did get me hope without issue.

 

Thoughts on what this might be?

 

My initial panicky ideas where that it could be some bad fuel?  Then I started thinking about the 13 year old 98k throttle pot.....

 

Anyone had this?

[stu8v]

I'd be more inclined to change the maf.

[Madmitch]

Agree with that.

[Nev]

[font="'arial unicode ms';"]Symptom: Idle revs hunting (and perhaps power seems weak[/font][font="'arial unicode ms';"]).[/font]

 

[font="'arial unicode ms';"]Check the following (in order of likelihood/simplicity/cheapness):[/font]

• [font="'arial unicode ms';"]A boost leak from your post turbo pipe-work, ideally perform a pressure test to 2 Bar.[/font]
• [font="'arial unicode ms';"]Possible MAF failure (a common problem), unplug it and test. If that helps then swap it out with a known working one and test. Be sure to replace with a genuine Bosch unit.[/font]
• [font="'arial unicode ms';"]Possible coil-pack failure, swap it out with a known working one.[/font]
• [font="'arial unicode ms';"]Possible spark plug gap/age issue. Check ceramics for cracks.[/font]
• [font="'arial unicode ms';"]Possible cracked intercooler (the vertical welds seams sometimes fail).[/font]
• [font="'arial unicode ms';"]Faulty throttle body (very rare) or TB to inlet manifold gasket seal.[/font]
• [font="'arial unicode ms';"][font="'arial unicode ms';"]Faulty loom affecting the MAF (extremely rare).[/font][/font]

Edited by Nev, 21 November 2016 - 09:25 AM.

[Horace]

Thanks chaps.  Will take that info on board.

[james_ly]

Water ingress on spark plugs? Has it been sat in the rain?

[Nev]

Water ingress on spark plugs? Has it been sat in the rain?

 

Mainly that just causes stuttering misfires, rather than regulated up/down cycling/hunting of revs which is what the OP has I think.

[Horace]

No water ingress.  Car lives in garage now, and problem occurred on a dry day.

[Mangham54]

Does the c20let have a crank position sensor? If so I wouldn't rule that out, the effects are the same but just a touch stinger. Had this on a 2.0dti Vectra, hence the suggestion

[Horace]

Took it to Jon Seal and he replaced the MAF on spec.  Was okay on way home (short journey).  Drove down to Suffolk for xmas and about an hour in, it started playing up.  Dropping from 70 to 50 with constant throttle position.  I change it down a gear and it hesitates and then picks up a bit.  After about 5 mins, it seems to go back to normal.  Then 15 mins later, it's at it again.

 

So I had an old coilpack hanging around, swapped that in, and symptoms are same (although I can't verify the serviceability of the coil pack as it is old).

 

I did notice that when I was driving up hill, it started playing up immediately, so maybe load related?

 

I now have an EML light on, but have not had opportunity to read codes.

Anyways, it's back to Jon this weekend....

 

Thanks Nev for list.  Will discuss with Jon (I'm no expert!)

 

I'm falling out of love with this bloody thing.  Just can't trust it.

[chickendippers]

Try giving the throttle body a clean, had similar symptoms on a few cars here

[siztenboots]

vacuum leak , cheap to fix , check for that first. or a split in the boost hose if its worse under load.

[Nev]

vacuum leak , cheap to fix , check for that first. or a split in the boost hose if its worse under load.

 

I agree, get them to do a 2 Bar pressure check of the post MAF pipework all the way to the TB.

[Horace]

Managed to get it the 10 miles to Jon's.  Drove like a pig.  Stuttering and hesitating, then immediately back to pushing me rapidly towards the horizon.  Tickover was all over the place, too high and hunting, then nearly stalling.

 

Would a vacuum leak affect the tickover?

[Nev]

Such a violent symptom should be an easy fix TBH. It's just a process of elimination, starting with the above list.

 

Symptoms of a vac leak is under-fueling and incorrect bypass valve actuation, the latter of which might cause some quite stark acceleration problems.

 

Surely now that you've handed it over to them again they can fix it without you having to worry?

 

Edited by Nev, 22 January 2017 - 02:39 PM.

[Horace]

Yeah, I'm not worried, but I do like to learn from the experience of the forum. 

[Horace]

So back to this......

 

Jon has had the car for a while now.  Next he changed the MAP sensor.  I drove the car home and it was ok for a couple of days, then started playing up again when hot.  Jon suggested he come and pick the car up with his mechanic Chris.  So before they arrived, I took the car out and gave it a good thrashing up and down the bypass for about 10 mins, so it was bloody hot.  As I came back into the village, it was back to its old tricks.  With poor hesitant throttle response and basically undriveable.

 

Chris swapped the coil pack (no change), the spark plugs (no change), so he limped it back to Jon's workshop.

 

Next they tried the boost solenoid which improved the drive but still getting splutter under load and a full misfire.  No change basically.

 

Then they got an eml code and changed the lambda sensor, .  Car improved a bit but was still very grumpy. 

 

Next they swapped the throttle body over (no change).

 

They're now clutching at straws and looking at swapping the injectors out.  This is the next step.  After that, they're looking at ECU.

 

Chris tells me they keep getting u2100 canbus malfunction error in opcom when reading codes. and it won't allow him to remove it.  Opcom tells him that I have a corsa-c z20let ecu and that's why he's thinking ecu issues.  The ECU was replaced by Liam at MMG some time ago, so I'm going to have a chat with him to see if he can shed any light.

 

Does anyone know where I can get Napalm?

[Nev]

Sheesh, get them to do the first point on my list.

 

They can also isolate the MAF (even if it's brand new) by disconnecting it and the ECU will run in open loop mode (thus eliminating it (and any possible wiring problem to it) from the list of culprits).

 

 

 

 

Edited by Nev, 15 May 2017 - 09:16 PM.

[The Batman]

I prefer the unedited version Hope you get it fixed soon bud maybe find someone with a spare maf or borrow one to save on costs

Edited by The Batman, 15 May 2017 - 09:02 PM.

[Nev]

I prefer the unedited version Hope you get it fixed soon bud maybe find someone with a spare maf or borrow one to save on costs

 

I know, I regularily find I have to re-edit once I've calmed down !!

 

 

Edited by Nev, 15 May 2017 - 09:15 PM.