Hi Everyone,

My 1991 740 Wagon (422,600 miles!) is having an idle problem that's driving me crazy!
Problem started about 2 weeks ago - car would start fine, but then as it warmed up (but hadn't "kicked down" yet) the idle would start to drop until the lights blinked like it was about to stall. Then it might bounce up again. And then it would drop too far. I would give it a little gas, and it would be ok. Once I put it in reverse or drive, problem would go away.

Then it started getting worse and I would have to give it gas for a longer period of time (up to 30 seconds to a minute). If I didn't it would stall.
Then it got bad every time I stopped at a light or a stop sign - idle would drop and drop until it was about to stall and I'd have to give it a bit of gas.
Some days it wasn't a problem at all!

Took it in and they said they cleaned out the air filter and what i think is called the air box? Said it started fine after that and I should be ok.

And it did start fine when I pulled it out of the shop...

Later that night problem started again.
Next day (yesterday) car wouldn't start. Would crank, heard the fuel pump, etc., but wouldn't start. Gave it a bit of gas, finally got it to start. Same thing happened some time later in the day. Took at least 8 cranks the second time to get it going.

Now it's back at the shop and they'll look at it on Monday...

Car's been well maintained, no leaks, have the oil changed every 3,000 miles. Recently had the fuel pump, filter, and regulator changed. Has a new battery, alternator, water pump, 5 year old timing belt, and a 4 year old starter. I am the second owner.

Any thoughts on what this could be??? I am at my wits end with it!!!

Also attached is a picture of the engine in case that might be helpful...

Thank you!!!!

 

remove and clean the throttle body, and the idle air controller, reinstall them, verify the IAC is actually working, verify the idle switch on the throttle body is closing at idle, and opening right off idle.

 

x2

Also sounds a bit like the cold start injector is on all the time or erratic. Just a thought here as I had similar symptoms on my old BMW and when I pulled the harness connector from the cold start injector (after the engine was warm) it would idle nicely.

 

later 7/9's did away with the cold start injector. I dunno if this one is one of those or not.

 

Hello,
I am new to the Forum and am no expert (so I may make some mistakes in my description of our problem) but our 1990 Regina 740 Volvo has been giving us many headaches with shaking and poor cold starts.

We have ruled out Cold Start Injector problems common in these models - our car was rewired according to the Service Bulletin 1990 (disconnect the CSI from the computer and rewire it to the starter). We had the injector checked, all the wires, and everything was good.

We still experienced an erratic shake at idle - especially on cold damp mornings. This, we thought, may indicate a short or faulty connection between the IAC, Throttle Switch or Computer when humidity is high.

We narrowed down our problem to the throttle switch. The symptoms indicate that either the new IAC valve is not getting a strong enough signal to open and shut and or the transition time between the IAC shutting off and Throttle working is not working correctly. It is almost as if the IAC is still on when we touch the throttle. There seems to be little information on the forum about symptoms and repair of this switch. (any links would be appreciated)

We first diagnosed the Volvo Throttle Switch using mode II at the code box. (pressing twice). As instructed, we manually triggered the first click of the throttle switch. LED flashed rapidly, then code 332 comes up. This indicates that the Throttle switch at idle was functioning as it should. But when we did the second test which requires us to manually open the throttle completely, also called Wide Open Throttle, we do not get the 333 code coming up. (We are not sure what fault this indicates and any help on this would be appreciated) However, if we went inside the car and pushed the peddle to the metal creating a WOT, code 333 does come up. Strange?

It seems obvious, that there is definitely a problem with the Throttle switch. We read they do malfunction. We have a brand new IAC, very clean Throttle body, and all other sensors and relays are new including MAP, Engine Temp, Air Temp, Relays, fuel pump relay, fuel pump etc.


The original Volvo Throttle Switch part number: 1-389 558-6 is no longer available. So far, we haven't replaced the Throttle Switch with a good used one (difficult to find but on its way). In the meantime, an old Volvo mechanic said try the Bosch Throttle switch (not made for Regina, but is available and inexpensive). We put in an old, but working Bosch Throttle Switch and it made a difference! But not 100%. The shake is still noticeable. However, we are now full of optimism, after months of trying to solve this problem, we are concluding that our mysterious shaky idle and cold start problems have indeed something to do with the Throttle switch.

With the Bosch switch, the car started this morning. It was a cool damp morning. Car reved up to 1100, dropped nicely to about 950 rpms. When we gave it a bit of gas, rpms didn't drop to almost dying as they used to with the original Throttle Switch. Unfortunately, the car did still shake a bit.

We still have to check the plugs and wire connections to the IAC and Throttle switch, but are optimistic that we have at least narrowed in on the problem.

If any one else has fixed this cool start, humidity related erratic idle with a new Throttle switch we would be grateful for information. Thanks!