Hey ozvolvo peeps,
I’m feeling a bit bummed cos I’ve gone and taken a pressure washer to my 740’s engine bay and now it won’t run right. Car is 1990 740 Turbo with LH2.4. I only got the car a couple of months ago and had been having a ball fiddling with it and tuning it up.
I’d troubleshooted poor idle, misfire, hard start, no boost issues already and it was running like a dream for over a month. I should have learnt my lesson as I’ve had bad experiences with pressure washers before.
When cold, car starts and will idle, if a little low, around 600rpm. I can leave it to warm up some, and the revs slowly slowly start to drop. If I apply throttle it will rev up, albeit misfire a bit. Then when left to idle once more, it will drop off and stall.
Once the car is warmed up, it will start but only run for a second before revs drop and motor stalls.
Initially, it threw codes for
3-1-2
Signal missing for knock-related fuel enrichment
Wiring break between EZK terminal 4 and FI #28
2-2-3
Signal missing to/from idle air control valve
Circuit fault to IAC or faulty IAC valve
Engine difficult to start; low idle speed
I realised the knock sensor had come unplugged so I cleaned sensor and plug and reconnnected.
I also cleaned idle air valve connections. I had already cleaned the idle air valve last month.
I reset the ECU and tried again. Codes were gone and it did seem to idle a little better. But still would drop off once warm and fail to idle when warm.
At this point I also unplugged and cleaned ECT and TPS and MAF.
I tried unplugging the MAF and idle would come up to about 700-800rpm and idle comfortably. But bog when throttle applied. Is that Norma when MAF is disconnected?
I then had a code for:
1-2-1
Signal missing or faulty to/from pressure sensor
MAP Pressure sensor
I assume that is for having unplugged the MAF?
I inspected wiring and did find a couple of wires that had slightly exposed wires on an injector and on the throttle position sensor plug so I wrapped them.
I also checked the throttle switch. Is clicking with slight move off closed. So that seems right.
When I clamp off hose from idle valve to inlet, the idle drops and then stalls so I assume it’s working?
I tried unplugging the O2 sensor while it was running but made no difference.
The main loom that runs kind of behind the alternator with the wiring for idle valve, knock sensor, ect, injectors is a bit of a mess and covered with lots of tape. I sprayed a bit of contact cleaner on the wiring and the next time I went to start, it cranked for about 10 seconds without starting (only time it did this). So I’m thinking that there is maybe a short or exposed wire down there somewhere?
I don’t know where my multimeter is so I haven’t been able to check any voltage or resistance readings.
The car is supposed to be going to a workshop this week for an exhaust (it doesn’t have one) and a roadworthy. But at this point I don’t know if it will make it. Don’t fancy paying a tow truck to take it 1km.
I feel like it would be beneficial to at least try another MAF and maybe another idle valve before I go digging around the wiring.
The way it seems to be fine until it warms up makes me think it’s related to ECT or O2 sensor but would they throw codes?
I did also change the oil just before I degreased so the O2 may have gotten a little bit on it from the filter? But I wiped it off with a rag.
The main thing I haven’t checked is is to see if there is a water in the distributor cos it’s a pain to pull. The way ignition is breaking up when revved makes me suspicious. That is my next port of call but would that cause a difference in ability to idle cold and hot?
Any advice would be appreciated. So disappointing when you put loads of hours into the thing to get it running right and then it gets ruined by the temptation to clean.
