1992 245 (LH2.4) Idle Problems, Missing, Rough Running,At 1000rpm+ Runs Great

[Build]

Hi Everyone,

Today with a warm engine, while driving my 1992 245 (LH 2.4) for 15+ minutes, it instantly started rough running/missing at idle, and
while accelerating slightly above idle. At 1000rpm + it runs great as always.

When the engine is cold, it idles and runs fine. After it warms, it idles very rough when driving. When it's sitting in park, the idle is fairly smooth with only slight intermittent roughness.

The throttle body is clean, TPS is working and properly adjusted, AMM (cleaned) and ECU are 6 months old. Anything 1000rpm+ runs strong and normal, regardless of temperature. I ran codes and got an all good 1-1-1.

I checked the ect resistance and voltage, works perfectly through its temperature range. I check the IAC resistance and voltage, working. Maybe I should try cleaning it?

I went over everything and there's no vacuum leaks anywhere. Checked vacuum gauge, 19-20lbs at rough idle, and solid smooth 21lb at 1000rpm.

I have a Bosch white label ECU 0-280-000-951 in the car. Tried my backup remanufactured Bosch unit and got the same results.

I check all ignition components and it checks good, cap, rotor, wires, coil. The Sparkplugs look good, consistent light tan color.

I'm out of ideas.

Any ideas are very appreciated. Thanks, Jim

[dj_v70]

You can try the computer diagnostics. You use the same box you checked codes with and put it into diag mode for IAC, fuel injectors.

Basically if your IAC is gummed up internally, you will still get good resistance/voltage. Running diag throws the IAC rail to rail and you can hear/feel it. If you don’t hear it, IAC isn’t working. Also, runs injectors in similar fashion. You can feel each injector to make sure they are vibrating, etc.

[Build]

Hey Thanks dj_v70,

How do I run the computer diagnostics? I ran codes in pin 2, and got an all good 1-1-1. Is this how I access computer diagnostics?

Jim

[dj_v70]

Jim,

A google search for Volvo 240 self diagnostics will point you to the right place. I just tried to find my Bentley 240 manual, but I must have trashed it. I got rid of my 240s a year ago after almost 30 years of ownership. Great cars if they wouldn’t rust;)

Even with 1-1-1 code you can still have faults that aren’t detected and hence the self diagnostic tests. The self diagnostic tests don’t produce codes, operator has to perform manual checks through hearing and by feel.

[dj_v70]

See this regarding diagnostics. viewtopic.php?f=2&t=24944

See control function 3. You still use socket 2, put you have to press button 3 times.

See control function 2 also and check throttle switch. If system doesn’t realize throttle is closed, it won’t activate idle circuit.

[93Regina]

warms, it idles very rough when driving. When it's sitting in park, the idle is fairly smooth with only slight intermittent roughness.....Anything 1000rpm+ runs strong and normal...

"Put the spurs to her, Chuck." ... The Right Stuff

[Build]

DJ_v70,

I ran function 3 diagnostics. The injectors seemed good. Maybe they aren't consistent with each other, I don't know, but seem to be working ok? The idle air control moves very quickly and firmly open and closed. I would guess this is good. When I cleaned it the other day, it had almost no residue in it, just a slightly tinted cleaner came out.

The sparkplugs look really similar in color and coating. The spark was fat and blue on all of them.

The throttle butterfly and switch is properly adjusted per Volvo. The ECU is receiving signal from it.

I continue to look for vacuum leaks, even on the newer hoses.

Other ideas?

Thanks, Jim

[dj_v70]

So, your saying it idles fine in park when engine is warm, but not when in 'D'. What are rpms while in park vs when idle while in 'D' when engine is warm?

Some other ideas:

a) When you checked plugs, was the engine idling poorly for awhile first? Else, that check might not help you. You can try disconnecting O2 and check voltage with voltmeter while it is running poorly. Recollection is that around .5V is good, close to 1V is too rich and close to 0V is too lean. I haven't done that in years, modern OBDII has spoiled me:) That might give a clue (lean would be vacuum leaks, obviously).

b) THE FOLLOWING CAN BE DANGEROUS AND GET YOU SHOCKED FROM HIGH VOLTAGE. You can try disconnecting one plug at a time while running poorly. Google how to do this safely (the way I do it isn’t safe!). You might have to disconnect Lamda-Sond first so it doesn't compensate (I forget for sure, been awhile). This troubleshooting technique is great for isolated issues to a single cylinder (spark, plug, injector, compression).

[Build]

DJ-v70,

Yes, when in park the idle is fairly smooth, just an occasional intermittent miss/roughness. When in drive or reverse it's drastic. I assume it might be the additional drag on the engine which isn't running well.

When I checked the plugs it had idled for probably a couple hours as I did tests.

I checked the O2 and the readings were in the .22-.94 range. I went ahead and installed a new one since my records show it had 80k miles on it.

I have every record of service and work this car has had since new. I purchased the car from the original owner in 2002. He owned my local Volvo dealership and it was his daily driver. He was a purist about Volvo. The car was as new. The seventeen years I've had it, it's been mostly perfect, and I've done all maintenance myself. I also have a XC70, yes the diagnostics are great, but in many ways prefer working on the 240. Cleaning the pvc on them for example.

I've got some insulate long pliers I could try the plug wires.

My gut feeling is there's a vacuum leak.

[93Regina]

gut feeling is there's a vacuum leak.

Engine is running a pinch lean....so, what's the fuel pressure, with and without vacuum line attached to FPR?

When engine is warmed up, SLOWLY clamp down on vacuum line going to FPR...what happens.