Hi all.

Driving back taking it easy on the motorway (sticking to the speed limits), I gave it a gentle bit of throttle and there was some wierd noise and backed off. At this point, the car seemed to be fine.

However, when we came off the motorway and pulled up to the traffic lights, the engine idle seemed to be very lumpy. I turned it off and tried to restart it and it was much harder to restart than normal. It sounds fine at more than 2500 rpm and it didn't appear to have lost any vast amounts of power.

I have checked the boost gauges at 1500rpm, and they seem to be pretty stable and not much fluctuation. Also, if we give it a bit of revs, it sounds fine but then dies down and sounds like its going to stall, before the revs rise and it idles lumpily again.

Any suggestions as to what else it could be? I've not had chance to take the plugs out yet and test the compression that way. Another possibility was the inlet manifold gasket, but that appears to be fine too (at least as far as I can see). There also appears to be no smoke that I can see? I've also noticed that it has sounded a bit tappy over the last few days. The ECU isn't showing any problems either and theres no lights lit up or anything?

Its running non-sequential turbos, intake, downpipe, decat, full system, AVC-R and PowerFC.

I've already checked both the MAP sensors and they're connected properly (i've already had this problem once this week). As far as I can see, all vacuum hoses are connected fine. I've also checked most of the other sensors, and they appear to be fine too. The PowerFC doesn't indicate anything out of the normal.

When i'm sat in the car, with the windows up there appears to be a tappy sort of noise from the engine bay. Peering into the engine bay, it looks like its coming from the turbo side of the engine, possibly by the lower intake manifold rather than both sides ( I presume that a worn or broken tip would make a noise both sides of the engine rather than just on one side). The car hunts between 1k to 1.5k, before finally settling at 800rpm (ish) after about 20 seconds. At idle, the vacuum reads a steady 12.5 inch/hg (about 320 mm/hg), which from what I can see from my search, is about right?

I've taken it for a drive, and it boosts exactly the same way as before, no visible smoke and is fine apart from in the lower revs, where it sounds a bit rough (sounds slightly like a misfiring car, but apart from a slight shudder, runs ok).

Is it possible that its a leaking inlet gasket, or a slightly knackered turbo?

 

Does it idle smoothly? 12.5 inHg is kind of low, but usually the RPMs will fluctuate and the needle will jump around at idle if you have a broken apex seal. Did it used to have more vacuum?

-Max

 

Once it gets to 800rpm, yeah, it idles smoothly. My bad on the 12.5 bit as looking again I know that it should be higher. I think before it was marginally higher, but i've not really noticed before today. When it is hunting for an idle, it appears to be around the 16.5 mark.

 

Also, i've ditched the airpump.

 

Any more advice on this, as unfortunately, I bumped the car about two days after the initial message and the car has only just gone back on the road after having a redesigned front end? Is it possible that a blown engine-turbo manifold gasket could cause it, as i've noticed some scorch marks in that area?

 

Engine-Turbo Gasket is more likely to be noticeable at High RPM, not at Idle.

I'd be pulling the plugs and running a compression check to start with.

 

I have to get it compression tested on the weekend, but i'm not looking forward to the outcome. The thing that confuses me is the fact that it appears to run absolutely fine, apart from the idle, and the fact that the exhaust is slightly noisier.

 

Mine is kind of making the tap tap tap sound too, I've been scratching my head about it for the last couple of days. Do post what you find if you get it figured out.

 

Welsh Dan,

I have exaxtly the same symptons as you (and mods for that matter + fuel upgrades). I'm thinking it's a cracked/chipped seal, but have yet to have it tested.

Low end torque is crap as a result but high end is still good, and I'm holding .8 bar from 3500-4000rpm onward (full non-seq conversion). Fuel consumption is slightly higher too, which is not good when we pay as much as we do in the UK

Before problem, idle was at 430 mm/hg, now 320 mm/hg same as you.

This all happened while the car was being mapped.

Oh well, new engine in order. Good time to get some internal work done

 

Oh, and the exhaust has a very raspy sounds to it... more so than usual!

 

my car has the same exact problem down to the T. It's at gotham racing right now waiting for steve to look at it. If you find out what is is post it back. They seem to think it's a chipped apex seal as well from turning it over and listing to the pulses.