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Old 03-23-2004, 01:58 AM
Join Date: Mar 2004
Location: United States
Posts: 7
Default 740 idle problem

I recently purchased a 1991 740. It has an idle problem that the local Volvo mechanic cannot figure out. Anyone out there with some ideas? The idle fluctuates regularly. When in park it will start at about 700-800 rpm and then about every 5 to 10 seconds it will suddenly drop to about 200-300 rpm, then suddenly jump to about 1200 then settle back to 700-800 rpm. It does this only in park. When in gear at idle the tach wavers a little but does not make the big jumps. The engine often stalls when the rpm drops. On a couple occasions it would not re-start. Also, on a couple occasions the engine would not start initially at all. In these no-start situations the car would suddenly re-start ok when left sitting for a day or two. When the car is running in gear on the road it seems to perform normally.

When the engine will not start, there is a smell of fuel after aperiod of cranking so the fuel delivery seems there. Also, on a couple of occasions when it won't start, in cranking it it would fire very breifly just as the key was being turned OFF. Could this be a problem with the ignition switch? As there are (apparently) no aftermarket repair books on this model I cannot figure out the starter and coil wiring. Maybe thefluctuating idle and the no-start problems are seperate?

The local Volvo mechanic tried swapping out the computer boxes, the air temp sensor, the air control valve. The vacumn hoses all appear good. The throttle body gasket is new. The knock sensor is new. The sparkplugs, wires etc. are recent and appear good. There are no codes on the diagnostic box. The mechanic also checked the fuel pressure (apparently at the proper psi). The car seems to run fine on the road, however, I am hesitant to drive it anywhere for fear it may do the no-start thing again.

Any thoughts or suggestions?

Peter Hunt (alias Admrudder)

PS - I have a 1982 240 that runs terrific - really reliable (CIS system), and is generally easy to work on. I thought the 740 would be a nice upgrade in style but I'm not sure on the reliability. Any thoughts on 740 (1991 Regina system) reliability? Are there any repair manuals available anywhere?

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Old 04-02-2004, 01:16 PM
Join Date: Mar 2004
Posts: 77
Default 740 idle problem

First of all, there is a repair manual out there. I know this because i just finished shopping around for one for my 240. Luckily i found that bentley publishing put out a manual specific for my car for a 10 year period, making it a very comprehensive manual. other than this, i didnt see many other model specific manuals, but i did see a chilton's manual for early 90's volvo's. While it is not model specific, it does cover 90-93 volvo models. I went back and checked and this manual does have your model of car. Unfortunately, chilton's from what i hear is not the best, but would be sufficient as a place to start for you.
Secondly, this sounds like either an injection, ignition or idling problem. Most likely from what I know it could be the idler motor. have u checked your spark plugs and fuel injectors for fouling and what not?
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Old 04-03-2004, 12:21 AM
Join Date: Mar 2004
Location: United States
Posts: 7
Default 740 idle problem

Hi Pilotsims,

Thanks for your reply! I am definately going to search out that chiltons manual! Thanks for the lead!

There is no idler motor on this but there is an idle air control valve - which is certainly suspect, however the mechanic replaced it with another "used" one he believed was good - it did not change anything.

I put new plugs in but did not put in new wires or dist. cap - they appeared really new. However, I have ordered new wires now to try that. I am suspecting possibly ignition in some form.

Maybe I'll get lucky with the new wires! I hope I hope!

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Old 04-05-2004, 03:51 PM
Join Date: Mar 2004
Posts: 77
Default 740 idle problem

Hopefully it works for you. good luck and if you ever find out what was wrong, id be interested to hear.
good luck!
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Old 04-29-2004, 12:21 PM
Join Date: Apr 2004
Location: United States
Posts: 1
Default 740 idle problem

Did you figure out the cause of your 740's idle problem? I have one that died on me on the road and will not start. I ckecked the fuel the FI RELY and the spark everything is good. But it developed a bad habit of stalling after the initial start in the morning and then idled sporadically. This behavior began about two weeks before it died in the middle of an interstate. Like yours, my740 has new plugs, wires, cap, rotor, and I'm stumped.

Thanks for any help you can give.

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Old 04-29-2004, 02:07 PM
Join Date: Mar 2004
Location: United States
Posts: 7
Default 740 idle problem

Hi, Walzilla,

I hate to say it but I'm glad I'm not the only one with the problem! Maybe the two are different but wow am I stumped!

I haven't followed up on my idle problem on this site simply because I have been too busy at work but here is my current situation since I last posted:

The car still isn't fixed!! I took it to another local garage that has a good reputation (but are not specifically Volvo mechanics). The lead mechanic could not locate the problem either. To date I have replaced or exchanged the following:

Computer units, knock sensor, temp. sensor, air meter sensor, idle air valve, speed sensor, plugs, wires, ignition switch unit (there was a thought that the no-start may have been related to a bad switch). Fuel pressure was checked (38 psi). Have I missed any sensors?? (car has Regina system). Intake gaskets replaced (possible vacumn leaks) etc.

The proplem is if anything getting worse. The car will not start intermittantly, when it initially starts it runs very rough and often stalls (sometimes not re-starting). After it runs a minute or two it will idle apparetly normally for a minute or so then suddenly drop in idle (to 200 rpm or less) then rise suddenly to about 1200 then settle down to 700 again, to be repeated at odd times generally about 30 seconds to 1 minute apart. Some times it stalls when it drops and will not restart.

I have not had it stall when driving however. but I have not driven it much because I don't WANT to get stuck!!

My last ditch effort is to bring it next week to a certified Volvo dealership garage (they said they have a mechanic who has never failed to solve a problem - we'll see!), however, I am way over in money into this car and if they cannot find it at a reasonable cost I am cutting my losses and getting rid of the car. There is a donation lot a mile from the Volvo dealer, if they can't fix it for a couple of hundred dollars (can you even GO to a Volvo dealership for less than $500?) I am driving it (if it starts) to the donation place and dumping it. Unless anyone reading this wants to buy it cheap?

Walzilla, yours could be any number of things but I think a failed Speed sensor or knock sensor would stop the car from running but still have spark and fuel (check the ground on the speed sensor - maybe it is just loose. I had a bad knock sensor that made the car hardly run). Anyone else have a thought?

Oh, yeah, I have NOT replaced my fuel filter yet - like a dumbie. Maybe it is dirt getting through - my first mechanic said that he checked the fuel pressure and it was good (I think he said 38 psi - I assume that is right) and that a clogged filter would show as lower pressure. But still...I am going to change the filter in a day or two when I get a chance. If it IS that I am going to kick myself all over the block - that should be the 1st thing changed I suppose!


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Old 11-08-2007, 12:08 AM
Join Date: Nov 2007
Posts: 58
Default RE: 740 idle problem

By chance do you turn off your air conditioning system before you shut down your engine? Also, when the controls are set to "defrost" it runs your air conditioner even when you have the fan set to "off". It just runs the fan at a low, sometimes inaudible speed.

Well, what I discovered shortly after purchasing (saving, if you ask me) my 740 that has similar but not exact idling problems is that there's a delay relay that helps save your compressor. You turn on your car and it keeps the compressor from kicking on until a few (fifteen i think) seconds after you start the engine.
Nothing is real, everything is permitted.
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