Dear Fellow Brickboarders,

Hope you're well. Am I right to conclude that consistent high idle (1,700 rpm) and poor fuel mileage (16-17/U.S. gallon vs. 21 [normal]) might result from a failed throttle position switch? Or, could the engine control unit (ECU) also have failed?

I've replaced: (a) the Idle Air Control Valve (IACV) with a known-good used unit, (b) the engine coolant temperature sensor, (c) the air intake temp sensor; and (d) the MAP (manifold absolute pressure) sensor. The only code is for 1-2-2, which indicated air intake temp sensor's signal was missing or faulty.

The in-service throttle position switch is factory-original, so doesn't owe me a nickel. The same is true of the ECU.

Now, I see a "check engine light" (CEL) on and after start-up. This is new. Only once has the CEL stayed-on after start-up. That was due to failed oxygen sensor.

I appreciate whatever pointers you deem helpful.

Yours faithfully,

Spook

Spook,

A while ago my car was telling me the MAP sensor signal was missing and I swapped it out with several MAP Sensors that I had as spares, but that did not help. So I thought that maybe the signals were not arriving in the ECU. Following the wires back to the ECU I discovered that four of the wires were cut somehow. Don't know if this could be your problem.

Regards,

Gus123

Dear Gus123,

Hope you're well. What you suggest is possible. The car is parked outside, so a "critter" could have gnawed wires. It's also possible that corrosion disrupts the circuit. I have the wiring diagram, so can trace the wires.

Thank you, for nudging me to do this.

Yours faithfully,

Spook

What codes are stored?

Hi Spook,

Look for any vacuum leak. I'd say the least expected leak could be from the brake booster's pushrod seal. As this seal only comes with new booster, test this seal first by spraying some carb cleaner around the MC/booster interface. If there's a leak the idle would change.

Hope this helps,
Amarin.

Dear Amarin,

Hope you're well. Thanks for your help. I used starter fluid, which consists of ether and other high-volatile hydrocarbons. I sprayed this atomized fluid on the seal between the brake booster and the master cylinder. The idle didn't change. I spready this fluid on the top of the charcoal emission canister. No change. I sprayed the hoses atop the intake manifold. No change.

It seems to me that an air leak large enough to change the idle speed - or to create "rough running" - would have to be pretty large, akin to having a vacuum hose cut or disconnected. Is this assumption sound? Or, can a hose crack allow entry to small amounts of air, which then disrupt normal engine function?

Thanks again for your help.

Yours faithfully,

Spook

Intake manifold gasket - Try spraying directly on the exposed edge of the intake manifold gasket with engine idling. The whole circumference. It took awhile but that is how I finally found the source of the high idling/poor mileage/noisy running in my 90 240 years ago.
--
Will I buy another Volvo??? We'll see....

Dear jwalker,

Hope you're well. Will do. It is hard to access the bottom edge.

I'll use starter fluid, which has in it ether and other high-volatiles, which should produce a pretty quick response. I wondered how a small a gasket leak could cause rough-running.

Thanks for the suggestion.

Yours faithfully,

Spook

Hi Spook,

Yes, there are places that are probably impossible to access. Do the best you can and good luck with it!

BTW - A small hole will only get larger. If it begins to sounds like a jet then you will definitely know it’s the intake manifold gasket!!
--
Will I buy another Volvo??? We'll see....

Dear Spook,

Based on your recent findings that there is no vacuum leak, I would go back to the Air Temp Sensor code 1-2-2 and look at it more closely. I think that for Regina the cummulative input from Engine Coolant Sensor + MAF sensor + Air Temp Sensor determines the amount of fuel needed by the engine.

Now that the engine idles high means a fairly lean mixture which for non-Regina cars usually indicate there's some vacuum leak. In absence of any vacuum leak I think THAT Air Sensor is the one causing lean mixture thus mimicking a vacuum leak condition. And lean mixture could cause misfiring.

Sensor cleaning might be in order. Can't think of any undue cause for it to fail, itself being situated far from engine heat being next to the air filter box plus its wiring harness is not subjected to much vibrations as to cause any internal failure. Could be needing replacement too if its due to age but I don't have much info in regards to this sensor.

Your recent replacement of the old ECU also helps to wipe clean those contacts so that part is ok. And the recent CEL could be in response to the lean mixture (i.e. not O2 sensor fault).

Amarin.

High idle is from extra air entering some where I would think the rubber o ring on the shaft may be missing , You could try to locate the leak by using starter gas to while its running to see if anything speeds up ??or slows done maybe its a loose fitting around the charcoal canister?

hi jay,
as you know, my 940 is a rex/regina but haven't ran with high rpm's. something you know already, but i didn't see in your description.

possibly throttle body valve stuck open, keeping the throttle position switched on?

probably not the answer, but it probably could use a good cleaning anyway.

regards,
byron golden
86 245
92 245
94 940

Hi Spook,

The only thing I have experienced that is somewhat similar was in an 89 244t and it was years ago so my memory is a little foggy.

The problem was a very high idle (over 1000). I don't remember if mileage was effected because it was a stick and that high idle pretty much made it undriveable.

I chased it unsuccessfully through the idle control motor before trying a spare ECU that I had from a parts car. The change of ECU solved the problem in my case.

Good luck and finding your particular solution.

Randy

Dear rstarkie,

Hope you're well. Thank you for your suggestion! I just swapped-in a known good Engine Control Unit (ECU), that I acquired in 2004 and tested before storing it.

The idle is still above 1,500 revs/minute. Thus, I don't think the factory-original ECU has failed.

The Check Engine light did not stay on after start-up. That may be the result of having disconnected the negative battery cable clamp from the negative battery terminal, while I swapped ECUs.

Is there any sensor, the signal from which - absent or weak - causes a steady high idle?

In the meantime, I'll swap-in another Idle Air Control Valve.

Yours faithfully,

Spook

replace the intake gasket,lately??are all the seals around the injectors good?

Also check that throttle body gasket. Maybe torn or leaking

Hi Spook,

"In the meantime, I'll swap-in another Idle Air Control Valve. "

You're fortunate to have one. I hear the Regina IAC valve commands a good price.

Usually high idle is the result of excess air, sometimes caused by a leak. While swapping the valve, you might consider blocking one port if it doesn't solve the high idle. If you block the air path through the IAC valve and the idle remains high, you have proved the excess air is not a result of either the computer controlling the valve, its wiring, or the valve itself, including the throttle position sensor. Just keep yourself mindful of where excess air could be entering the engine: manifold gasket, hoses, throttle plate, brake booster hose ...

Sounds like the high idle is a recent development. Accompanied by poor mileage makes me think the air is not being measured by the MAP sensor. No, I'm getting out of my depth with little experience with malfunctioning Regina.
--
Art Benstein near Baltimore

I got a job at a bakery because I kneaded dough.