Idle Issues The Same Before and After Fuel Pump/Filter Installed

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mphilleo
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Joined: Fri Oct 18, 2013 11:21 am
Year and Model: 1988 Volvo 244
Location: Lincoln, ND

Idle Issues The Same Before and After Fuel Pump/Filter Installed

Post by mphilleo »

Just to start from the top, I've got a 1991 Volvo 940 with the B230FT. I just got done replacing the fuel filter and feed pump, some other deferred maintenance. It now starts to start on the first crank, instead of the 2nd, and idles more smoothly.

I went through and manually confirmed no obvious vacuum leaks. I calibrated the throttle actuator lever to ensure that it was not keeping the throttle plate slightly ajar and ensured the stop screw was in the correct position. I also confirmed the TPS was calibrated in the correct position (I did not test it with a multimeter). For good measure, I cleaned the quick disconnects for the AMM, IAC and TPS. The following is what I discovered.

Regardless of whether it's cold or warmed up, the engine wants to idle at around 1100-1200 RPM and will idle at about 750-800 RPM in Drive or Reverse with some vibration. I discovered that unplugging the IAC did nothing to the idle, positive or negative. After plugging the IAC back in, I unplugged the AMM and found that the idle lowered ever so slightly, maybe 100 RPM, as best as I could tell with my ears. If I plugged it in quickly, the idle resumed at the usual 1100-1200 RPM. However, I noticed that it hesitated briefly when I took too long to locate the pins when reconnecting it. So as a test, I allowed partial connection and it killed the engine. For what it's worth, with the IAC or AMM unplugged, although never simultaneously, there was no harm to the engine running when I applied throttle under the hood.

Obviously, there was some issue with fuel delivery before, because it will turn over the first time, cold or warm, and the vibration issues in Drive or Reverse are somewhat lessened. It would appear that there is something wrong with the base idle, but to think the IAC and AMM are both faulty (or at least don't help or hinder the engine) is remarkable to me. Frankly, I don't want to consider the possibility of replacing both, since I've been in the process of reconditioning the car for a test drive, which could mean more issues. Any suggestions are welcome as always.

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93Regina
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Post by 93Regina »

mphilleo wrote:wants to idle at around 1100-1200 RPM
Word for the day - Air...it takes air to make it idle that fast.

Throttle plate must be spec'ed to their specification.

Otherwise, your IAC is stuck open (knock on it when running), air is being sucked in via intake manifold, etc., and/or idle switch is not adjusted.

benpineapple
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Post by benpineapple »

I agree with 93Regina, definitely air delivery.

Remove the IAC, the rotating piece on the inside should pivot very freely when you move it. If not, bathe the thing in TB cleaner and scrub the heck out of it. I had similar idling issues that were traced back to the IAC. Do you have any issues with idle speed while coasting?

Did you replace the fuel filter/pump because of these symptoms?

If I were you, I would play around with other throttle plate calibrations as well.
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mydamnvolvo
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Post by mydamnvolvo »

Yes. Air. Does it start when hot? Also, when you are sitting at a light, does the rpm gage wiggle?
Current:
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mphilleo
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Joined: Fri Oct 18, 2013 11:21 am
Year and Model: 1988 Volvo 244
Location: Lincoln, ND

Post by mphilleo »

Thanks for all the thoughtful input, everyone. Just to clarify, since I bought the 940, I have only been doing preventative and baseline maintenance. I haven't had the chance to drive it any more than on and off the trailer when I brought it home. So it was definitely a pig in the poke.

Anyway, I took the time to make sure the MAF was absolutely clean (even unbolted it from the air filter cover) and cleaned both ends and all wires with MAF cleaner. I re-checked all hoses providing vacuum to the intake manifold and the intake manifold gasket passed a cursory visual inspection, for whatever that's worth. Then I double checked and re-calibrated the TPS and idle stop screw to Volvo's specifications and I think it helped. The odd thing about the idle screw is that with the TPS properly calibrated, the idle screw, even if backed out to the point of not touching, wouldn't drop the idle to 480-520 RPMs, so that couldn't be helped. Furthermore, I noticed the idle was wandering a tad, so I took a rubber mallet and gave the IAC valve a few taps and, wouldn't you know, it smoothed out. It took a few more applications of the hammer to keep the result consistent, but I think that was a factor in my issues. This was sort of puzzling to me, because one of the first things I did was take it off and give it a good bit of carb cleaner and used electrical cleaner on the contacts for good measure. I also got into the holes with a few q-tips to wipe off excess carbon/sludge.

Overall, the idle is a good deal smoother than before, but the only thing that perplexes me is that regardless if it's warm or hot, the engine wants to maintain 1100 RPMs +/- 100 RPMs in Park only. In Drive, it's just about spot on at 750 RPMs. The only thing I've noticed is that when it's in Park, before shifting into Drive to test engine load, the application of the brake pedal seems to cause a 100-150 RPM drop in idle speed. The hoses coming to and from the master cylinder appear to be secure and in decent shape, so I don't know if that's a factor. Lastly, the idle is also fairly smooth when in Drive, but I do hear a bit of metallic vibration, which I'm unsure if it's something like a heat shield or the exhaust, which does have a muffler leak. Lastly, I don't know how old the gas is, or if it's premium, but I put in the corresponding amount of Techron FI system cleaner, which probably helped somewhat. Fresh gas with the remaining cleaner may be of more help.

That's about all the new information I have right now. I plan on registering and insuring it tomorrow, so I may find out more then.
mydamnvolvo wrote:Yes. Air. Does it start when hot? Also, when you are sitting at a light, does the rpm gage wiggle?
Yep, it now starts on the first try cold and also starts great after being warmed up. The tachometer seems to be pretty steady, but there's that metallic vibration occasionally that I mentioned above.

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93Regina
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Post by 93Regina »

mphilleo wrote:IAC... the engine wants to maintain 1100 RPMs +/- 100 RPMs in Park only..
IAC Fix-It

OEM specs on throttle plate and idle switch - No iffs, ands, or buts.

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