I really need help with a bad idle problem on our immortal 1991 745 Volvo with the Regina system and 188,000 miles. Problem: when cold, car is extremely difficult to start, will repeatedly stall, occasionally backfire; with persistent efforts it will get running but repeatedly stall until very warm; when running or driving, it lacks power. In addition to myself, two mechanics have worked on the car and between us we have either replaced or substituted with known good components each of the following parts which all remain on the car: radio suppressor relay, fuel pump relay, Regina coil, crank positioning sensor, fuel pump, fuel pressure regulator, idle air control (mounted under the manifold), checked unsuccessfully for any vacuum leaks, and last weekend we replaced with a new Bosch unit the Coolant Temperature Sensor (CTS). The timing belt and associated components were replaced about 14,000 miles ago and seem to be in good shape. The throttle positioning sensor looks okay and the throttle body itself was served by Volvo several years ago. Problem persists.
Any help from each and all would be most dearly appreciated, with a special plea to Art B and Spook!
Heartfelt appreciation, Larry

Put some new NGK. plugs. Check you plug wires and rotor Resistance Ohm. Rotor should be 1k. I' be seen old weak plugs stall .when idleing.

Larry 21, you there? Is it fixed?

I have a similar prob w my 1990 745 w Regina. I'm re-reading all posts, gonna use the info to go over mine this weekend. I'll let you know how I do. Someone on BB said aged 740s need to have the fuel tank at least half full. I'm trying that too.

Hi,


Check ignition timing and cam timing. Does the idle better with the addition of fuel, or does it stay lumpy?


Goatman

... I would also say check the OBD codes as listed in the FAQ.

His first post in nine years.

Well, Larry21, how is it going? Have you remedied the problem?
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Considering the symptoms, and what you've already replaced, I would suspect a faulty O2 sensor.

Is the engine timing ok ? How about the exhaust system? Partially blocked, maybe? Also , have you checked the fuel pump connector for corrosion ( big pink wire especially) located under carpet, above wheel well left side, in trunk area? my 2cents.

Hi Larry21- 2 things on my 92 740 made it run/idle something awful: the coolant temp sensor (which you replaced) and the spark plugs. You didn't mention them but if they are bad (or only 1 is) it can make a huge difference.Won't cost much either. Check your on-board diagnostic for any clues there. Hope it gets running better !------------------- Tinkerbelle

Another thought - when I started to have troubles with our '90 744 TI a friend suggester that I take all connectors apart, clean them if possible, then add dielectric grease and zip tie any that I can.

I also checked and cleaned grounds - keep in mind - if a component does not have a ground wire, it gets its ground by its attachment to the engine or chassis. Engine ground straps can cause problems - check them and add an extra for good luck.

BTW - when I had troubles with my anti-lock brake light coming on sometimes when I hit a bump - it always went away on the next start-up - indicating a bad connection - my dealer kept my car for a week, pulled apart under the dash and in the trunk and even substituted the anti-lock controller from the service writer's car to try to find the problem.

I was only charger one hour's labor - they did ask me to replace the panels that they had removed.

Have you read the FAQ?

Have you checked for codes - all sets available?

I would have tried a dealer after one replacement part - They only charge one hour's labor, and I have never had them repair or replace more that one part in over 500K Volvo miles!

I really like to repair almost everything in my cars or around the house, but sometimes you need expert help.