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What Components Control Idle? 700

posted by slowboat on Thu Oct 21 08:37 CST 2010
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last visit: Sun Jun 22 13:19 CST 2014

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I posted this question weeks ago in the 900 section but no one has responded. I hope someone here can help since 740/940 are basically the same.

I have a '93 945 Turbo (B230FT) that has had a cold idle problem for 2 years.

After recently replacing the MAF, the car is consistently running fine and the sometimes erratic idle has improved.

However, now that it is fall and morning temps are in the 30s-50s the idle surge is back.

Here are the symptoms:
Car sits overnight and starts on first crank 100% of the time. Idle is steady. I drive away, stop at a red light 3 blocks from my house and the idle surges between 600-900 RPM for about 10 seconds. It evens out and idles fine for the rest of the day. If it is colder, it surges longer and the idle does not even out unless I'm driving and the engine warms up a bit. I have also found that if I start the car and let it idle for a few minutes before driving away, it will surge. This happens in winter if I start the car and have to scrape ice or brush snow off for a few minutes.

Here's what I've replaced:
- Mass airflow sensor (MAF)
- main fuel pump and fuel filter
- cap, rotor, plugs (NGK copper)
- swapped idle air control valve***
- oxygen sensor
- all vacuum lines
- cleaned flametrap
- cleaned throttle body
- ran seafoam through intake

***I must qualify the idle air control valve swap. I have 3 IACVs. They are all used and I have cleaned them all. The car runs exactly same with any of these 3. I believe they all are in good working condition, but maybe all 3 are flaky?!

When a Volvo shop replaced the MAF 2 mos. ago, they checked fuel pressure, ecu, engine sensors, looked for vacuum leaks and found nothing unusual.

What am I missing here?

Chris
'93 945T 191K

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What Components Control Idle? 700

posted by Farm Boy on Tue Nov 16 03:04 CST 2010
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last visit: Mon Oct 28 07:35 CST 2013

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I agree that it sounds like a TPS, but I drove two bricks 300k miles and never had a TPS fail, which makes me not want to suspect the TPS.

What I DID have fail several times through the years was the intake manifold gasket. Multiple air leaks there will cause a surging idle, and the condition will change as the engine and manifold heat and cool at different rates, expanding and contracting.

If you have never replaced your water temperature sensor by #3 cylinder, consider doing that while the manifold is pulled back and it is easy to get at.

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What Components Control Idle? 700

posted by Steve on Thu Oct 21 10:11 CST 2010
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last visit: Fri Oct 24 07:16 CST 2014

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Check the continuity of the throttle position sensor as well: easy via instructions in the FAQ.
--
See the 700/900 "FAQ" at the menu bar top screen left side.

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Definitely a TPS-related problem 700

posted by slowboat on Thu Nov 11 05:59 CST 2010
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last visit: Sun Jun 22 13:19 CST 2014

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OK. The surging calmed down on its own but now the idle is high.

When I start the car, the tach zooms to 2000 RPMs and settles between 1200 and 1500 RPMs. When I put it in gear, the engine idles around 1000 RPMs.

Here's what I discovered:

TPS checks out OK for continuity (instructions per FAQ).
When idling high, disconnecting and reconnecting the TPS wire harness does not change the idle speed.

Jiggling the plug at the TPS changes the idle.

If I pull the TPS wire harness hard toward the firewall, the idle drops down to normal and stays there until I turn off the car and start it the next time.
So, every time I start the car I play this game-- 1. Turn key. 2. Pop hood. 3. Yank wire (idle drops). 4. Close hood and drive away.

I have not adjusted the TPS. I still hear a faint click when turning the throttle pulley.

I suppose I should pull the throttle body and TPS and try to adjust per the FAQ.

Do you think the TPS is junk or out-of-adjustment? Or could there be a wiring problem?

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Definitely a TPS-related problem 700

posted by Will740turbo on Mon Nov 15 18:44 CST 2010
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last visit: Wed Oct 22 16:09 CST 2014

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Definitely! I had issues with my TPS not working because one of the pins popped out of its socket and disappeared out the back of the pigtail. Pull the rubber boot off the back and make sure the wires are all attached - there should be three.

I wouldn't adjust the TPS it's a pain and it's usually unnecessary. Jiggling the plug points to wiring issues.
--
1990 740 Turbo, on its way to stock specs, maybe beyond

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What Components Control Idle? 700

posted by aleekat on Thu Oct 21 08:57 CST 2010
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last visit: Fri Oct 24 13:19 CST 2014

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My guess is an airleak. Intake manifold gasket? As the engine changes temps, manifold expands and contracts with temps.
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Post Back. That's whats makes this forum work.

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