[ShirleyG90]

Hi guys,
Having a mid-life crisis and bought myself the car that 20 year old me wanted. Zero mechanical experience, hadn't even changed a tyre when I bought my 1990 JX Sierra. No concept of what I was getting myself into - car drove fine, thought I'd just be on the hook for some cleaning and tidying - in actual fact I'd bought myself a tired little Swift GTI (I think MK2) wrapped up in my SJ70, which after a month of driving decided to idle at 3k rpm. I took it to a local mechanic, who said the cold start valve was faulty and he blocked it off, said just to give it 10mins to warm up then all should be fine but then it started bogging down whenever I'd apply throttle, and in the end got so bad it would just stall whenever I'd try to take off. After much fussing about reading the million and one posts about high/low/erratic idling, then testing and cleaning all the things, she now idles at an excruciatingly low 100-300rpm (even with the air bleed screw almost all the way in) and stalls at the smallest hint of throttle...
I understand this is an air/fuel mixture issue but I can't seem to work out what exactly is going on. I can see it's common practice to delete the cold start valve so I'm wondering what has gone horribly wrong here for me.

Things I have done so far:
- checked for vacuum leaks (none)
- cleaned the throttle body
- cleaned the MAF sensor (did not touch the delicate wire)
- cleaned the iacv
- tested the TPS sensor (within spec - "kind of", when I do the adjustment procedure I can't seem to get it to sit at OL)
- tried to get the error codes off the ecu but the previous owner butchered the loom so can't find the monitor coupler and even with the diagnostic ports bridged at the ecu, the CEL does not come on - I don't believe the CEL has been integrated with the swift wiring properly.
- checked the spark plugs (fine)
- changed two fuel filters and one fuel pump (have a pull, push setup with a small surge pot). I changed the pump at the tank, because I thought it sounded like it was labouring, but the new one makes the same sound so it was a bad guess - fuel delivery doesn't *seem* to be the issue, although I haven't done a fuel pressure test.

Before I rage quit and pull the entire thing out to start from scratch (ie. get it reconditioned + new loom) - does anybody have any suggestions on what I should try next? I'm reluctant to go buying a bunch of new parts without knowing for sure that is the issue/s (learnt that lesson from the fuel pump exercise).

TIA

[UBZ]

You need to sort the wiring and pull any codes from the ECU . A bad MAF / TPS / water temp sensor / o2 sensor etc or a bad wire between could cause the problems your experiencing . .
Is it a mk1 or mk2 Gti engine ? How has the distributer been setup with an angle drive to fit?
I put a Mk1 in a SJ413 , the wiring was not super difficult , but I remember being told not to cut / join / shorten the sensor wires as they were impedance calibrated.
Also from memory you need that cold start valve in the system. It has a wax heated element off the coolant system that allows / restricts airflow based on temp , and the ECU map is expecting that airflow especially at idle.

[ShirleyG90]

Thanks for the reply UBZ. Sorry I didn't see this earlier but after lots of frustration I had to take a break as it was doing my head in
Feeling ready to try again now...
Ok that's interesting about the shortening/joining of the sensor wires as that is exactly what I had to do as a previous owner had cut the o2 sensor wire at the ECU leaving only about 4cm which I then joined and re-ran the new wire to a new o2 sensor. So this could be adding to the misery. I'll try again to get the codes off the ECU somehow.

Cheers.

[Gwagensteve]

The 02 sensor is not referenced at idle. It 100% won’t be causing your issue and the car will run with it unplugged. In early EFI cars it’s just used to tune air/fuel at cruise for economy.

In my opinion, the “you can’t shorten the loom” stories are from people who have never done a conversion and/or use the story to tell you to stay carby. I’ve shortened/modified very loom I’ve worked with. The only wire that even looks like it can’t be shortened is just screened to prevent interference.

First step is to ensure the check engine light is functional and check for trouble codes.

When the car is idling spray brake cleaner/ether around the engine (away from the intake) and listen to changes in rpm. Odds are you have a vacuum leak.

[ShirleyG90]

Ok, thanks Gwagensteve. That's kind of a relief as the entire loom has been modified/shortened and also good to know about the o2 sensor. To be fair it was running fine for the first month without the o2 plugged in, so that all makes sense. Yeah the situation with the CEL is frustrating. Out of the ECU, the CEL wire is snipped and terminated along with the other two diagnostic wires. I bought a little LED so that I could emulate the CEL dash light without actually wiring it up properly, just to get the codes in the first instance. But I must be doing something dumb because it's not working how I imagined. Will have to go back to the wiring diagram.
As for the vacuum leak suggestion, if I can get it to idle I'll try again and listen for changes, but at the moment, idling is so low it stalls and dies pretty quickly. Many thanks again for the advice.