'92 240 rough start

[Swiftfingers]

Lh2.4, m47 swap, 1992 245.

I'm having a hard time tracing this one down.
My 240 has rough starts, both warm and cold. It'll crank for a second or two before it starts, then it'll idle low (4-500 RPM) and rough for 2-5 seconds before the idle will pick right up to about 900. Sometimes it'll stall on a cold-start if I don't crack the throttle. Runs like a dream once it's been on for 5+ seconds.
Any ideas?

 

[OVERDRIVE]

What's your battery voltage while off and when cranking? Mine did this for a couple weeks then the battery died. I suspected that the coolant temp sensor was getting a poor reading when you first turn to key position 2. I'd check the coolant temp sensor's resistance at the LH module's plug too. Also check that you still have the ground from the valve cover to the firewall.

 

[Swiftfingers]

Ground strap is intact.
I'll check the voltage, but it cranks strong.
Do you know which pins are the coolant temp sensor, and what the range is?

Additional info: I have a fresh coil, plugs, rotor, button, and cap.
Also, it's 2024, here's a video:

 

[Nagrom]

Are the recent problems after the swap? Or has the swap worked for a while and now it's shit the bed?

 

[Swiftfingers]

Are the recent problems after the swap? Or has the swap worked for a while and now it's shit the bed?

It's been doing this since I bought it.
it's really not a huge deal, I just crack the throttle to get it to start, then it's fine.

 

[Nagrom]

Make sure it has the appropriate ECU/EZK boxes.

 

[Pietercc]

What is the check engine light for?

 

[Swiftfingers]

What is the check engine light for?

There's a CEL that goes away as soon as the revs pick up, I don't think I can pull a code for it, can I?
The "service" light is just triggered by the odometer.

Make sure it has the appropriate ECU/EZK boxes.

I'll grab the numbers off them in the morning.

 

[esmth]

I don't think that tach is reading correctly. it sounds much lower RPM than it reports. Also, on a cold start you should be getting at least 1200 rpm for a moment on LH 2.4. I think the throttle body/idle stop is set up too tight.

 

[shoestring]

I'd also look at throttle body return to base settings and TPS reset.

Please don't tell me the IAC is bypassed.

 

[Swiftfingers]

I'd also look at throttle body return to base settings and TPS reset.

Please don't tell me the IAC is bypassed.

IAC is intact, and makes noise when I run the diagnostic.
TPS clicks when I barely move it, not sure if there's more to check there.

What is the check engine light for?

Both ECU and EZK read 1-1-1

Make sure it has the appropriate ECU/EZK boxes.

What's your battery voltage while off and when cranking? Mine did this for a couple weeks then the battery died. I suspected that the coolant temp sensor was getting a poor reading when you first turn to key position 2. I'd check the coolant temp sensor's resistance at the LH module's plug too. Also check that you still have the ground from the valve cover to the firewall.

I was reading about 490 ohms on both the ECU and EZK for the ECT.

 

[dl242gt]

Uh Oh, pink label 561 means you really can't trust anything about that fuel ECU. Try to find a 951 as that is the upgrade replacement Volvo provides.

 

[Swiftfingers]

Uh Oh, pink label 561 means you really can't trust anything about that fuel ECU. Try to find a 951 as that is the upgrade replacement Volvo provides.

Bingo!
Swapped in a 951, and she fired right up!
I'll give it a few days before I officially say "case closed", but it seems to be running well.
Thanks a bunch for the suggestion.