Idle help 91 SHO!

[Jason Gardner]

Needing little support on an idle problem! My father is a mechanic at a shop and hasn't had a lot of time to figure this problem out so my car still sits in the driveway It started doing the surging rpm's and occasionally stall out after giving it throttle. The father hooked his scanner to it and it brought up that the Air Charge Temp Sensor and Idle Air Bypass Control Valve were both faulty. We changed both also doing the plugs, plug wires, valve cover gaskets and intake gaskets while we were in there....But the thing still idles as it did. When he tries doing an idle test on his scanner it resets the scanner back to the beginning of the koeo test.
He has talked about maybe there being a relearn on the computer and maybe that's what it needs but has been too busy to search how or what needs to be done so I have taken it upon myself to see if I can get my baby out of the dive way soon! Any fast reply's on how or what to do would be appreciated.

 

[Pintony]

Hello Jason,
Does your SHO run normally off idle?
Does your SHO have an IACVM idle control motor?
Just spitballing here...

http://www.ebay.com/itm/IAC18-OEM-I...ash=item3f4b75d4a7:g:OAQAAOSw~otWcwFj&vxp=mtr

 

[SHOdded]

How long has this issue been happening? Could definitely be an IAC issue. You could get away with cleaning it if it's dirty, but the usual fix has been a new unit. Could also be a faulty TPS, check the voltages on that. Have you tried unplugging the MAF to see if there's any difference vs with MAF connected? Are the EGR nostrils clean? Did you have occasion to replace any spark plug wiring or to take off the intake manifold? Would check for frayed/pinched wires if so.

You can get the codes for yourself using just a paperclip and counting the CHECK ENGINE flashes:
http://web.archive.org/web/20090917070939/http://www.shophoenixproject.com/eec/eec.htm

 

[Jason Gardner]

Hello Jason,
Does your SHO run normally off idle?
Does your SHO have an IACVM idle control motor?
Just spitballing here...

http://www.ebay.com/itm/IAC18-OEM-Idle-Air-Control-IAC-Valve-Motor-/271848952999?fits=Year:1991|Make:Ford|Submodel:SHO&hash=item3f4b75d4a7:g:OAQAAOSw~otWcwFj&vxp=mtr

Yes the car runs fine at driving speed it's just when I come to a stop and the car has to idle it then surges and stalls at times. We did change the iac motor.

 

[Jason Gardner]

How long has this issue been happening? Could definitely be an IAC issue. You could get away with cleaning it if it's dirty, but the usual fix has been a new unit. Could also be a faulty TPS, check the voltages on that. Have you tried unplugging the MAF to see if there's any difference vs with MAF connected? Are the EGR nostrils clean? Did you have occasion to replace any spark plug wiring or to take off the intake manifold? Would check for frayed/pinched wires if so.

You can get the codes for yourself using just a paperclip and counting the CHECK ENGINE flashes:
http://web.archive.org/web/20090917070939/http://www.shophoenixproject.com/eec/eec.htm

Issue started about a few weeks ago. The iac motor has been replaced that's the code it was throwing on the dad's scanner. When the MAF is unplugged the car will die also tried unplugging the iac motor and that kills it also. Forgot to mention we also replaced the vacuum hose that plugs near the iac motor it was very soft and crumbling from heat but still have idle problems.

 

[Pintony]

Issue started about a few weeks ago. The iac motor has been replaced that's the code it was throwing on the dad's scanner. When the MAF is unplugged the car will die also tried unplugging the iac motor and that kills it also. Forgot to mention we also replaced the vacuum hose that plugs near the iac motor it was very soft and crumbling from heat but still have idle problems.

OKAY... Based on your statement Jason. Maybe a smoke test to find a vacuum leak...
Visually inspect the hoses. Look for one that has an acute curve in it, it may have cracks.
Sticking EGR maybe or one with a bad diaphragm.

 

[Off Road SHO]

You might have more vacuum leaks in other hoses and the IAC valve is trying to compensate.
Check your vacuum at idle. I don't know what it should be at idle but your Dad will.

Tom

 

[Pintony]

You might have more vacuum leaks in other hoses and the IAC valve is trying to compensate.
Check your vacuum at idle. I don't know what it should be at idle but your Dad will.

Tom

18 inches of vacuum@idle is good.

 

[rubydist]

I have had new iac valves on SHO vehicles bad right out of the box, so do not assume that the new iac is good. In fact, I suspect your new iac is also sticky and causing the problem.

However, it can take up to a week for the pcm to "learn" the proper default pulsewidth for the new iac, so I would drive it for a week before I replaced it again. And, yes, I am familiar with the "idle reset procedure" and have never had it do anything constructive on any of the SHOs that I have owned.

Question: Did the code for iat go away after you changed that? Because I have never seen a SHO run correctly with that code.

 

[Jason Gardner]

I have had new iac valves on SHO vehicles bad right out of the box, so do not assume that the new iac is good. In fact, I suspect your new iac is also sticky and causing the problem.

However, it can take up to a week for the pcm to "learn" the proper default pulsewidth for the new iac, so I would drive it for a week before I replaced it again. And, yes, I am familiar with the "idle reset procedure" and have never had it do anything constructive on any of the SHOs that I have owned.

Question: Did the code for iat go away after you changed that? Because I have never seen a SHO run correctly with that code.

Apparently his scanner wont even connect to the car to get a code on it again. Keeps saying to check the connector that it isn't connected. Will probably have to end up pulling the codes again manually. I'm hoping I don't have to pull the intake off again to get that damn iac motor off unless there is an easier way to get to that bottom bolt. Will go inspect all the hoses as they also suggested tomorrow.

 

[Jason Gardner]

OKAY... Based on your statement Jason. Maybe a smoke test to find a vacuum leak...
Visually inspect the hoses. Look for one that has an acute curve in it, it may have cracks.
Sticking EGR maybe or one with a bad diaphragm.

Is there a specific place to look for vacuum leaks? We changed one that connected near the iac motor went down to a T connector think it was the fuel vapor canister purge valve then down to another T under the radiator.

 

[SHOdded]

Apparently his scanner wont even connect to the car to get a code on it again. Keeps saying to check the connector that it isn't connected.

ruby?

 

[Jason Gardner]

ruby?

Sorry don't understand what you are asking.

 

[Off Road SHO]

Key needs to be on.

 

[rubydist]

obd1 scanners are notoriously inconsistent - I just count flashes and don't even bother with the code reader for these cars.

 

[luigisho]

obd1 scanners are notoriously inconsistent - I just count flashes and don't even bother with the code reader for these cars.

Agree 100%

--and I have 2 different OBD scanners that are supposed to handle OBDI. They stink on these cars

 

[Jason Gardner]

Ok went out and did the paperclip test to pull the codes. What I got if I counted correct was 3 codes. 121, 124 and 179. Looked up the codes and the first 2 pertain to the TPS. Would that be the cause of the crappy idle and is there a way to test if that is the culprit?

 

[SHOdded]

More likely the codes are 21, 24, and 79, all separated by 1's. 1989-91 SHOs had 2 digit codes. UNLESS a 92+ ECU has somehow been installed.

 

[rubydist]

the codes will not all be separated by a "1" so that's not it.

121 and 124 will not result in crappy idle bouncing around unless the tps signal bounces around so the pcm is moving the amount of fuel up and down. you can test that by unplugging the tps and checking if that smooths out the idle speed (note that it won't drive right at all with the tps unplugged).

can you confirm the code on the pcm please?

 

[Jason Gardner]

Ah ok yes thats how I thought it looked when flashing but when came to search the codes the ones I found were with the 1 in front. To end any confusion I'll video the flashes tomorrow to help get some clarity. There were few times were it got confusing to me.