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Old 10-29-2013, 11:45 AM   #1
volvo 4 life
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Default 1988 volvo 740 idling high after new IAC valve

My dad recently purchased a 1988 740 with a five speed and after 2 weeks it developed a problem where after driving the car for a little while it will idle really high (2500 rpm) like the iac valve is stuck completely open. I hit the valve with a hammer when it was doing this and the idle came right back down to normal so I assumed it was a problem with the valve. Now we replaced the valve and its doing the same thing. Is it possible the valve is bad again or is there something else that would be telling it to idle high?
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Old 10-29-2013, 12:20 PM   #2
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Check for vac leaks, and clean out the hoses leading into the IAC. Also, clean the electrical connector to the IAC.

Check your base idle as well.
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Old 10-29-2013, 12:35 PM   #3
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tps switch , if it is out of adjustment or bad it won't activate the TPS when the throttle is at closed position. If the TPS checks out then it could be a fault in the ECU if there was a dead short in the original IAC valve and took out the hybrid circuit in the ECU.
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Old 10-29-2013, 01:25 PM   #4
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Check the throttle linkage length.

Although it would be better to adjust TPS and throttle stop before doing this. Easier to do with throttle body off the car.
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Old 10-29-2013, 01:49 PM   #5
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I will check the tps adjustment. When it idles high like this and you shut the car off it is sometimes very hard to start afterwards. I had luck holding the throttle to the floor and cranking it but it seems like it floods itself.
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Old 10-29-2013, 02:18 PM   #6
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PULL THE CODES.....
http://www.brickboard.com/FAQ/700-90...neOBDCodes.htm
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Old 10-29-2013, 04:01 PM   #7
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1988 should be LH2.2. No codes in that case, ECU doesn't have a CEL or store fault codes. Good luck , internet repairing a car = impossible.
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Old 10-29-2013, 04:55 PM   #8
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Quote:
Originally Posted by andysbeta View Post
1988 should be LH2.2. No codes in that case, ECU doesn't have a CEL or store fault codes. Good luck , internet repairing a car = impossible.
^^ * YUP * ^^

a late production or Califas/EGR car *may* be LH 2.4...
never underestimate the power of missing information...
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Old 10-29-2013, 06:48 PM   #9
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I believe it's 2.2 but I will check when he gets home.
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Old 10-29-2013, 10:14 PM   #10
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Originally Posted by volvo 4 life View Post
I believe it's 2.2 but I will check when he gets home.
if it is fitted w/a (last three digits of the part #) "007" Air Mass Meter then you're in
LH2.2 land......the LH2.4 meters have " 016 " on the tail end...
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Old 10-30-2013, 06:22 PM   #11
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Realized something else. When the car is warm it's really hard to start. What's the chance of the coolant temp sensor being bad? Seems to make sense because it would increase fueling and raise the idle if it thought it was cold right? And that would make it start hard warm and idle high.
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Old 10-30-2013, 06:43 PM   #12
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I had a 2500 RPM idle on my '87 740 turbo when the IAC valve died. I was 500 km from home too, made starting out really exciting with an automatic. Shift to drive, CLUNK! WHEE!

Replacing it with a non-busted one from a junkyard made everything happy again. It sounds to me like you just got another broken one or something's not hooked up right.
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Old 10-30-2013, 07:34 PM   #13
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Originally Posted by slipstream3d View Post
I had a 2500 RPM idle on my '87 740 turbo when the IAC valve died. I was 500 km from home too, made starting out really exciting with an automatic. Shift to drive, CLUNK! WHEE!

Replacing it with a non-busted one from a junkyard made everything happy again. It sounds to me like you just got another broken one or something's not hooked up right.
Those guys are easy - just block off the IAC hose and dial-an-idle with the hand valve. Not ideal, but works until you get it fixed and safer than trying to drive w/ a 2k5 idle.
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Old 10-31-2013, 07:20 AM   #14
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The iac valve wouldn't cause a hard warm start though right?
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Old 10-31-2013, 07:55 AM   #15
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Quote:
Originally Posted by volvo 4 life View Post
The iac valve wouldn't cause a hard warm start though right?
As far as I know, it shouldn't be the IAC causing hard start, no. The ECU 'ignores' the O2/lambda/IAC until a few moments after the car starts, if I remember correctly.
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Old 10-31-2013, 08:29 AM   #16
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That's what I thought too. Makes no difference if I unplug the valve to try and start it either.
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Old 10-31-2013, 10:00 AM   #17
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tps.
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Old 10-31-2013, 10:20 AM   #18
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check for cracked spark plug wires. almost always the culprit of a rough idle. even if not cracked, could be worn out, change em if you haven't done so in last 5K miles
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Old 10-31-2013, 10:28 AM   #19
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Plug wires last more than 5k.....
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Old 10-31-2013, 11:32 AM   #20
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When it runs it runs fine, no rough idle. Hard start and high idle are the symptoms. Think I'm gonna try and replace the coolant temp sensor and see where that gets me.
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Old 10-31-2013, 11:34 AM   #21
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Originally Posted by atrokz View Post
Plug wires last more than 5k.....
Not if they touch a hot manifold they won't. I know, I just went thru a set. didn't even make 5K
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Old 10-31-2013, 11:39 AM   #22
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Quote:
Originally Posted by andysbeta View Post
tps.
NEVER underestimate the proclivity for owners to fire the
parts cannon....sooner or later we'll all find out if it IS
an LH2.2 car and also * if ADJUSTING THE TPS helps *

...why .. it's just as plain as the nnnnoooossse on yer face...


OMG! it's a DICK!!.....
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Old 10-31-2013, 01:48 PM   #23
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It is a 2.2 car. The tps clicks right before closed throttle, it's adjusted fine. Maybe the tps is bad, but I have no way of knowing whether it is or whether it's the coolant temp sensor or iac and so on. I already have a coolant temp sensor from another car so I'll try that first.
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Old 10-31-2013, 08:55 PM   #24
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Quote:
Originally Posted by volvo 4 life View Post
It is a 2.2 car. The tps clicks right before closed throttle, it's adjusted fine. Maybe the tps is bad, but I have no way of knowing whether it is or whether it's the coolant temp sensor or iac and so on. I already have a coolant temp sensor from another car so I'll try that first.
TPS is a simple snap switch. VOM on it will tell you if it's working. Temperature sensor is a bit tougher (they're not completely linear), but should be around 3Kohms at 60F and 400 Ohms when the engine is warm.

I think '88 still has the needle valve for idle air at the throttle - make sure that isn't wide open. Check for vacuum leaks as well, though I don't think LH2.x will compensate sufficently to allow running with a hole big enough to get 2500RPM. For the IAC I'd say get a toothpick and see if you can open/close the shutter easily (you should be able to). There's also a test where you apply voltage to the contacts (one is neutral, one open, one close) - but I'm not sure what the voltage is. Probably +12V, but best to check first.

Last edited by saq; 10-31-2013 at 09:16 PM..
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