I've been slowly bringing a 91 740 Wagon (regina) that was sitting for a long time back to driving condition, and I have a strange issue I haven't been able to nail down. Every few days, all the sudden the RPMs will increase as I'm driving without hitting the accelerator, and it's always accompanied by a CEL. First time it happened it scared the **** out of me, so I pulled over and made sure the throttle wasn't stuck open (it wasn't) and pulled codes. I got a code 1-2-3 (ECT signal) on pin 2 and code 1-4-4 No load signal from fuel injection system on pin 6. Reset the codes and car ran fine for another 2-3 days, when all the sudden the same thing happened, RPMs start going north of 1500 while I'm at a stop light and CEL illuminates. Pulled over and had the same codes, reset and it drove fine again. Car was fine for almost a week when it happened again this morning. This time I reset the codes and got about 8 miles before the problem returned and the lights came back. I was nearly home so I just drove it carefully with the RPMs surging, but the issue went away about 2-3 miles before I reached home and car was driving normally again. This time I got the same two codes + 2-3-3, IAC signal.

I've already replaced the IAC so I'm thinking this may be a ground/wiring issue somewhere, especially as its so intermittent. Any common places to start checking? I've already checked most of the engine compartment connectors by unplugging them and looking for corrosion/broken wires but everything seemed fine. I checked all visible grounds I could easily see and cleaned up a few points to see if that will clear it up. Fuel injection relay was replaced several weeks ago when I bought the car. I was having a hesitation problem when I frist go the car, but that was solved with a new fuel pump and filter. Based upon my research, sounds like the only other thing it could be is the ECU. Anyone had experience with this issue before? I can't find a lot of information explaining the 1-4-4 code. Also seems strange the 1-2-3 ECT code only appears with the 1-4-4 code present.

 

per https://www.volvoclub.org.uk/faq/Eng...tionFaultCodes 1-4-4 is an ignition module code, indicating the 'load signal' from the ECU to the ICU is not present.... the ECU sends this signal to the ICU under heavy throttle/load conditions so the ICU can appropriately modify the ignition timing. the table gives several possible reasons for this (transpose Regina and Rex for LH and EZK in your case).

I'd be closely inspecting the engine wiring harness including where it connects to the Regina ECU and Rex ICU (I believe both of these are under the dash in the passenger footwell area) as well as the various sensors and actuators (ECT, IAC)

 

Thanks for the advice. I know the ECU is there, not sure where the ICU is but I'll pull the kick panel and see if I can find it. I may try swapping the ECU with my known good one as well as this happened again twice yesterday after posting, so the problem is getting worse.

 

So I started the car and wiggled the connection to the ECU in the passenger kick panel. RPMs immediately began increasing so I shut it down. Pulled the connector and noticed some corrosion on several of the pins on the ECU. Cleaned everything up with some fine sandpaper, blew all the crud out and reconnected it. Now when I wiggle the connection it continues running normally. Hopefully this was the problem, if so it was a nice easy fix 🙂