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240 [SOLVED] leaky injector? Rough cold start, runs rich and surging idle for 30ish seconds, then fine.

edited June 3 in Troubleshooting
1990 LH 2.4 Wagon has recently started to rough idle, run rich and surge for the first few moments after a cold start. Only lasts about 20 seconds. A sustained rev on 2K rpm makes its go away in about 10 seconds. Idles and drives beautifully after that, but have definitely noticed increased fuel consumption (not sure if that's the T camshaft I swapped in recently).

To me it seems like a leaky injector? before I disassemble the fuel rail, just wondering if anyone else has any other things to check, maybe some sort of sensor I'm unaware of?

(car has new plugs, leads, rotor and cap, fpr, maf and all new hoses. cleaned flame trap, iac valve, throttle body and intake. engine looks, sounds and runs great, no smoke. haven't touched fuel pumps, injectors or fuel filter.)


  • carnut222Greg S (@carnut222) Daylesford VIC
    My 91 does that sometimes - basically seems like it starts and runs rich and almost is missing on a couple cylinders - then I can rev it and it sort of “clears its throat” then idles fine...lemme know if you find the cause as I’ve been chasing it for a long time...a lot of people say change the ECU coolant temp sensor, which I haven’t done due to the access being difficult, but when I change the coolant next time I will do it. I checked the ohm reading for the sensor back at the ECU and it was OK, so I doubt it will make a difference...
  • Leads all plugged in correctly? Mine started doing a similar thing when the silicone elbow on the lead from the coil to distributor cap pushed the lead out a bit. Did the same thing on one of the plugs once too.
  • 240240 (@240) Canberra
    Are there any fault codes on the LH2.4 diagnostic box?

    It could also be a vacuum leak, so it's worth going over all the hoses, seals etc.
  • Hmm.. its definitely getting worse, running a bit more rough. Starter seemed slower to turn over this morning as well.
    Will get stuck into it in the next couple days. cheers for the tips.
    (I also had no idea about the 2.4 diagnostic box. Awesome. nice to know as I don't have any scanner tools etc.)
  • only code 2-1-4 on EZK (rpm sensor intermittently missing) - did have my crank sensor replaced a couple months ago. code might not have been cleared.
  • carnut222Greg S (@carnut222) Daylesford VIC
    Hmm.. its definitely getting worse, running a bit more rough. Starter seemed slower to turn over this morning as well.
    Will get stuck into it in the next couple days. cheers for the tips.
    (I also had no idea about the 2.4 diagnostic box. Awesome. nice to know as I don't have any scanner tools etc.)

    How’s the condition of your battery? Slow starter may be battery on the way out...
  • edited April 9
    hmmm... battery is all good, few months old. (starter is probably a separate problem - hasn't happened again! :tired_face: )

    tested the coolant temp sensor cold and the readings are within spec. I might pull and test the idle air valve too.

    Is there a way to test for leaking injectors without bench testing?

  • Does your car have a cold start injector?
  • yeah, mine seems to be covered in a lot of gunk. I unplugged it to see if that would make a difference, but nope. could be leaking though. Are they prone to failure?
  • You mentioned you tested the coolant temp sensor whilst it was cold, what about when warm? It could be running on cold mode full time which is why you are using more fuel now. Cold mode runs the injectors for longer than when warm. What do the spark plugs look like? Pull them while it's doing the rough idle
  • Yeah I'll get stuck into that tomorrow. pull the plugs and injectors etc. and test the temp sensor warm.

    Its worst in the morning regardless of weather/temp, which makes me think maybe fuel is leaking into the cylinders overnight and flooding the engine before startup. A few revs clear it out then it's good for rest of the day.
    There's actually heaps of threads online with these symptoms and none of them are really resolved. Could even be ecu.
  • carnut222Greg S (@carnut222) Daylesford VIC
    You’ll be a hero if you solve this one @buddyglitch
  • edited April 9
    Not to Hijack the thread, watching and learning because I'm also experiencing various issues with different cars of this era. The question of leaky injector made me think of an issue I'm having on an 89 740. Runs and starts perfectly if it's been used in last 6-12 hours. Leave it about 2 or so days and she farts and makes a show for about 10 seconds with a bit of smoke, mostly black.

    I assumed this must be a leaky injector, but doesn't make sense to me that it does this after say 2-3 weeks of sitting when the leaked fuel would have evaporated.

    Runs like a charm if used daily.
  • @carnut222 haha! I'll never sleep properly again until this car starts smooth!

    I had a similar thought after not driving my car for a few days @ToomanyVolvos . I know the main fuel pump maintains pressure even after shutoff. Perhaps there is still enough pressure to slowly leak fuel past injectors even when the car is just sitting?
  • Do a compression test and see if coolant is leaking in overnight due to a blown head gasket
  • edited June 3
    Okey dokey, much has happened since this thread, but I have fixed the problem! Starts up and idles beautifully, even on these recent freezing cold days. To summarise: If you have the above problem, try changing the IAC valve AND the coolant temp sensor together.

    It's my understanding that after troubleshooting, these parts were both miss-communicating due to being old and out of spec. Neither part had completely failed though.

    - Checked OBD codes 1-1-1 (all good).
    - First I replaced the coolant temp sensor (why not.. cheap part).. cold start still rough.
    - Using the OBD tool, I pulled a "faulty IAC" which was odd. It didn't exist when I had the old coolant temp sensor in.
    - Replaced the IAC valve with a cleaner one pulled from wreckers. Clear the OBD codes, start car and check for new codes. 1-1-1 (none).
    - leave car overnight and cold start. Starts are up straight away and runs beautifully (steady idle around 700rpm).

    Testing with a multi meter proved the resistance values were a bit off, but not by a huge amount. The old idle valve was also holding a steady idle (albeit slightly high around 950). Idle would drop erratically if unplugged, which proved the valve was functioning at least?

    Anyway.. moral of the story: LH2.4 will have you chasing your tale, so if it's been in there for 30+ years, try replacing it and see what happens.
  • edited June 3
    I should also mention, changing the temp sensor is a 5-10 min job. There is no need to remove fuel rail, intake etc. And it can be done without spilling barely a drop of coolant.

    - undo coolant cap, squeeze top rad hose to create pressure and then tighten coolant cap. This creates a vaccuum in the coolant lines and prevents spill when removing sensor.
    - undo tps sensor connector to allow access for 19mm long socket with 6" extension.
    - unplug white bosch connector and remove and replace temp sensor. (There is very minimal ratcheting space, but I've found all it needs is a 'crack' and the rest can be turned out by hand.)
    - undo coolant cap to relieve pressure then re-tighten.

  • carnut222Greg S (@carnut222) Daylesford VIC
    Thanks - good tip on how to replace coolant sensor without draining coolant and removing other bits! :)
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