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Badly running engine 
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Joined: Tue May 17, 2016 9:48 pm
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Location: Selkirkshire
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Post Badly running engine
Anybody any suggestions.... Engine in son's K3 not running well. Starts ok most of the time, but revs fluctuate a lot at idle. Todays wee problem is that he is struggling to keep the car going steady. Description is it feels like it accelerates and then brakes itself.... eventhough still trying to drive up a hill!!! :(
Thoughts are maybe fuel pump? Lamda sensor?........ suggestions appreciated


Tue Feb 13, 2018 11:45 am
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Joined: Thu Jun 27, 2013 11:32 pm
Posts: 358
Location: Norfolk
GTM: K3
Post Re: Badly running engine
Hi this may or may not help
What engine does he have in the k3
Is the inlet manifold a plastic one
and a plastic Throttle body
on my k3 when i did the engine change
It hade a plastic throttle body and my car would not idle Well
i found the plastic throttle body it had gone out of shape warped i think air was geting in
See my post
paul-s-k3-t2686-180.html

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Last edited by catsam on Sat Feb 01, 2020 10:50 pm, edited 5 times in total.

Tue Feb 13, 2018 9:47 pm
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Joined: Sun Oct 19, 2014 10:10 pm
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Location: Bristol
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Post Re: Badly running engine
I'd have said unlikely to be lambda - my lambda failed and it just made it run very rich but other than a black exhaust and a very rich smell it ran fine. Could be fuel starvation, or possibly just some iffy petrol - could some water have got into the petrol? Blocked fuel filter? or could be ignition. If its a dizzy engine (mems 1.9) or early VVC (mems 2.0) I'd be looking at the ignition leads.

Hopefully something simple


Tue Feb 13, 2018 10:28 pm
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Post Re: Badly running engine
The throttle body is a good call if plastic, they are often a problem.


Wed Feb 14, 2018 11:09 am
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Post Re: Badly running engine
Fluctuating revs in the dark ages of no computers almost always points at an air leak in the inlet manifold. So the throttle body is a good call. If that dosnt show a fault then the next cause is the fuel delivery. Again in the dark ages it was usually dirt in the carb, so now it could be an injector fault. once that checks out ok all that is left is the spark, again in the past a cracked spark plug could give these symptoms.


Wed Feb 14, 2018 12:52 pm
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Joined: Tue May 17, 2016 9:48 pm
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Location: Selkirkshire
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Post Re: Badly running engine
Cheers..... plenty to go on there and hopefully its not too great a job!!!!


Wed Feb 14, 2018 2:50 pm
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Post Re: Badly running engine
My immediate thought was an inlet air leak too. You might try spraying liberal amounts of WD40 around the throttle body and inlet manifold while it is running. I'm not sure exactly why this works as a very short term fix - whether it temporarily seals any holes or richens the mixture I don't know.

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Fri Feb 16, 2018 3:20 pm
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Post Re: Badly running engine
Check fuel pump


Fri Feb 16, 2018 8:43 pm
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Post Re: Badly running engine
Rather than start a new thread, mine started doing something similar, generally driving okay but a fast and fluctuating idle.

Did your son's K3 problem get sorted Phil?

I had a bit of fun diagnosing mine. I'd swapped in a complete 160VVC engine including gearbox, ecu, engine loom and all ancillaries a couple of months ago and hadn't used it a great deal with the onset of winter. It seemed to be running fine and was a noticeable improvement over the 143 (but that did have very low compression on 2 of the cylinders so suspected HGF across 2 fire rings). My first decent run on the "new" engine was a 270 mile blat across to Wales and over the Brecons and back for the Kitnet Christmas run out to Bethlehem (see this months CKC for pics). Towards the end of the run the idle started to become erratic and I noticed at the cafe stop that the exhaust was very black and sooty. It was a bit lumpy at idle and low revs but fine when opened up and pulling strongly. It got gradually worse on the drive home and the idle speed had crept up to around 2k and was surging from about 1800 to 2200.

I started by thinking vacuum leak and I did find that where the plenum joins to the inlet ducts there was some black silicone that had been smeared around the join so a definite clue of a previous owner having a similar problem. Taking the plenum off I found the gasket in three pieces and a lot more silicone crudely attempting to join them up. It seems it had worked to a fashion for a while but was breaking up and letting air in. I had a spare gasket in the shed as one had come in a head gasket set I'd bought a while back and not used as the original one was fine. I cleaned up the faces and installed the new gasket thinking what an easy diagnosis and an easy fix this was and at the same time patting myself on the back and cursing the bodge of the previous owner of the MGTF I'd taken the engine from (or their garage!).

Unfortunately, firing it up again I found it to have improved a little but still idling too fast and the revs surging.

Being confident that my sealing of the plenum to inlet manifold was sound I turned my attention to other things and my thoughts turned to MAP sensor, Idle Air Control Valve, Lambda sensor and Throttle Position Sensor. Typically my OBD11 reader wasn't working so having an OBD socket for the first time ever on this car since going to MEMS3 wasn't any help (I tried my reader on the daily driver to confirm it was the reader and not my wiring of the socket!)

I had a spare Lambda so I tried changing that next. No difference. I also had a spare TPS so swapped that, no difference. If I pulled the plug on the MAP the idle did drop back to 950 but a bit lumpy but went back high again after turning it off and on again. Possibly the MAP then. I also clamped the air hose into the IACV and this also settled the idle back to 950rpm. Possibly the IACV then...

I remembered having an old plastic inlet manifold that came with a big box of bits when I bought the car so turned the shed upside down looking for it. I found it eventually and it was MEMS 3 and had the right MAP sensor and IACV still fitted. I swapped these over and, no difference!

So, I'm scratching my head and decide it is time to leave it for a while, sleep on it, and try again another day. In my mind I'd sorted the the vacuum leak and I'd tried alternative Lambda, TPS, MAP and IACV. I guess it is possible that the alternatives I'd swapped in were duff too but it seemed unlikely. I came back to vacuum leaks. If the plenum to inlet manifold had been bodged it was clearly possible that the inlet manifold to head could have been too so resolved that would have to come off. I had to order up a new gasket in readiness as I know I didn't have one of those in the shed!

The following weekend my suspicions were quickly confirmed. Two of the fixing nuts were missing altogether (the top ones that go over studs). I'm not sure how much these actually do but I wouldn't have left them off. Taking the manifold off there was a small tear/bit missing in the top of the gasket on one inlet port hole and no corresponding piece stuck to the manifold. There was however a large chunk of old gasket still on the manifold near the jiggle valve port even thought the current gasket was intact at that location. Clearly the installer couldn't be bothered to clean up the faces before fitting the new gasket. The gasket had also been fitted low on the head face such that at the top it was projecting well into the air flow and only a couple of mm actually clamped between the mating faces. It didn't take long or much effort to clean up the faces and to carefully align the new gasket and hold it still when positioning and tightening the manifold. They do seem to want to droop down so you do need to support it until clamped.

With everything back together it fired up straight away and idled perfectly. I tired swapping the various sensors and it works fine with them all so I know I have a set of spares if ever needed but it seems that vacuum leaks are far more likely to be the cause of symptoms such as this.

I didn't get a chance to go out for a run then but this morning I did. Running sweetly and pulling very strongly so I'm happy again but still cursing whoever did the work previously. There was a receipt in the file of papers that came with the MGTF for a full head gasket change and new cambelts and water pump only about 10k miles before I'd bought the car. Done by a supposed MG specialist. I'm guessing it was this garage that had bodged both gaskets in the inlet so I'm now worrying about the HG itself. Compression is excellent though and no oil/water mixing so hopefully it is okay. Time will tell!


Sat Feb 01, 2020 9:37 pm
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