Hi all, I have an MOT booked next week and she's not running right. Any help would really be appreciated. Something seems to be up with either the ISV or blue temp sensor. The car idles poorly, cuts out at low RPM and smells like it's running rich. I tried a new temp sensor with no luck and then I noticed the ISV wasn't buzzing with the ignition on. If I lightly tapped it, it would buzz for a bit and then stop again. I tested the cable and seemed to get a stable 10.65V and so I ended up replacing the ISV. Still no success. I read somwhere that you can switch the black and blue cables temporarily and try that and that seemed to work for a bit. A 5min drive up the road and no issues. I have several of the blue temp sensors to test but nothing seems to work. Now when I tried switching the cables again, it didn't work the again the same way. I'm clearly lost and running out of ideas. I'm assuming its an electrical issue but it's been so strange to diagnose I really can't say. I also tested the throttle potentiometer as described in the Haynes and that seems correct. Anyway, any advice would be really appreciated. Jack
Check the ecu plug, the power supply plug near it, and the plug on the MAF for corrosion / dodgy wires
Hey, Thanks for the reply. I checked ECU plug and MAF and all seemed to be okay and I went through most of the wires I could see, cleaning up contacts and checking for splits. The ISV didn't buzz but I wanted to do a test drive and sure enough it was working perfectly for 15 mins. I pulled over when the engine was warm, turned it off and turned the ignition on. I felt a slight buzz for the ISV and measured 10.85V this time. I drove home and suddenly it bas back doing the same issue again. Do you happen to know what voltage the ISV should be getting? The next thing I was going to try was checking all along the ISV cable for issues. It's all tied in quite deep but I'm running out of ideas. Thanks
Regarding the blue temp sensor - unless you get a genuine one, you can be put through the ringer as from what I hear, anything other than genuine is not going to work properly and will just torment you. On my 8V (and granted it didn't fix the issue), I did find some iffy wiring around the ISV - cabling to the connector and a couple of poor earths which I repaired and heat shrank and then taped. The ISV connector is just a 2-pin so it might be worth getting some electrical contact spray into the connector in case there's any rust/corrosion that may not be visible to the naked eye. Might also be worth locating a second connector just in case there is something going on in there - I think they are a relatively standard connector so a new one should not be too much of an issue to source. As far as I know the ISV gets a solid 12V, you are getting approximately 11V which should allow it to operate but it does appear to be dropping out which looks like a poor connection. It will probably be ballache but I would also open up the engine bay loom and inspect everything - the wiring whether we like it or not is several decades old and is subject to degradation over time. Don't use insulation tape when you are retaping, get proper loom tape, it offers better protection and heat resistance overall. I hope this helps. Robert
Thanks Robert, There is definitely no issue with the connector on the blue temp as I even cut it off and put the bare wires on the sensor pins directly. (I needed to fix the wire and thought it was one less thing to troubleshoot) The current temp sensor is Hella which I'm told is quite good, in any case, I have about 5 different branded ones now and none of them stop the issue. They also read correctly on the OHM temperature chart so I don't see how that can be the case at this point. Looks like opening up the wires will be the next step. I wasn't aware of the loom tape so that's really good to know! Thanks for the help Jack
have a read of my troubleshooting guide: https://clubgti.com/forums/index.ph...ose-and-tune-your-mk2-digifant-gti-8v.124949/
Thanks all, I had a chance today to take a look at the car and unfortunately I am still stuck with an ISV that doesn't buzz. My MOT failed and it seems my CO2 test failed too. The car smells like petrol when the engine runs so I assume that means it's running rich. Rubjonny, I have read through your guide previously and there were a few things I didn't understand. First, I have a 1991 GTI California. Engine code RV I think. I don't think I have a WOT switch and some other parts of the throttle body seem different. Which holes are supposed to be plugged? I followed the Haynes and all of them should be correct but I don't believe any are plugged? Currently the car seems to be driving okay aside from running rich. The ISV doesn't buzz with the ignition but I think it runs when the engine is on. Hard to say with the vibrations. Stupidly I didn't check the battery this whole time but it was actually flat. It was only bought 6 months ago and I never saw the warning light, nor had any issues turning over. No idea what caused it but since the recharge it seems to run better. Rubjonny, If you see this btw, I would just like to say thank you for all of your posts on here as they have helped me out a bunch in the past!
All looks standard enough Digifant. I see wire repairs to the temp switches, are they definitely OK? Same with the vac hoses, and blanks? If you have an MFA , there's a vac line up the clocks too. You block this hose iirc, to the throttle body, for setup. What's that for? No sign of a switch back there?
yeah the california spec cars are slightly different, they use a TPS rather than a pair of throttle switches and the setup procedures are a little different. fo one thing it has diagnostics capability which is nice if all the basic checks come back ok from my troubleshooting guide the next thing I'd look at is the lambda probe, and try the reset procedure as described in the bentley https://vwts.ru/vw_doc/eva2/FU01/ch8.html
Yes that was me trying to diagnose it I believe that has something to do with using the petrols fumes. I forgot the term but its in the Bentley. It connects to a carbon canister I think. Yea when the bloody thing works . To be fair it has helped me out a few times but nothing at the moment. new lambda was fitted in the summer. that was actually spotted by the diagnostics. Thanks all for the help. I think I will need to go through everything again more thoroughly starting with Rubjonny's guide. I'm a driveway mechanic and it's currently -18C outside which means I will need to get back to this in the Spring/Summer. I will keep this updated though when I have more time and maybe it will help someone else in the future.
