High idle (2500 RPM) problem

Red '89 SC

Registered User
I have a 89 SC, 135k, 5-speed, haven't had any significant problems until now. It was running perfectly until I went through a car wash with those high pressure under carriage washes. Turned the car off when I entered...came out with RPM at 2500 or so, and it settled to about 22-2300. Turned it off, and the tach zipped to 0 awful quick while the engine slowly shut down. Heard a hollow, "howling" type noise as it did. Started it up a few more times, same result, let it sit for a hour or so and tried again, same result.

Had it towed, mechanic is telling me it's a primary control module (the engine computer?)...and that it needed to be sent back to the manufacturer for a re-build as spares are no longer made or available. Pointers?
 
there are 2 sensors on the throttle body. the bigger one is the Idle Air Control Valve (IAC). go get a new one of those from either Ford/Mercury($100) or i've had luck with the Advance Auto ($70) brand too.

let u know how it goes.
 
No honking goose sound after the motor shuts off.

Just saw the mechanic...they installed the re-built PCM/ECM and he said the car runs fine. IAC was fine according to him. BUT (of course) now I have some addl codes, so we don't know if it's the computer or something more.

Original codes were:
98
63
12
33
13
77

After re-built PCM/ECM installed, remaining codes are:
72 (MAF)?
22 (Baro)?
33 (EGR)

Mechanic is installing another MAF to see if it clears the codes, and looking for vac leaks. Just amazes me that one instant, the car was smooth as can be, and after a car wash, I am out $1500+ so far.

I now understand the love/hate, SC addiction...
 
$1500 wasn't just for the PCM, but included several other minor things I had been putting off for a while (front suspension R&R, windshield motor pump replace, tune up (plugs and wires), etc). I think the PCM itself was around $450 plus labor...I wouldn't know if that's a good price or not.

Let's just say that I recently put in $2k for a paint job and other cosmetics, so this could be the straw.
 
SC's are strange cars to a normal mechanic. they will totally guess at wuts wrong with it when they really have no idea. if i had a high idle i would never guess bad ecm.

wut are your codes for ?

u should try changin out the IAC despite wut ur mechanic said.
 
dude i would have given you the computor and any parts you need make a list of what you need ill check if i have em and you pay shipping theyare yours.
 
Thanks for everyone's info and advice. I have had my '89 SC since '93 but she's spolied me w/ no real issues until now. I have only found one good SC mechanic back in CA, but am now in N VA and found this guy through another local SC owner. We'll see how this pans out.

Thunderkid84: codes were pulled from the old and new PCM. I think I will go ahead with the IAC like you and others have advised.

MannySC: IAC, PCM, DIS, rear side speaker covers (grey), emergency brake (hand brake), balancer, auto dimming rear view mirror, antenna motor, stick rims, headlights, right rear body panel (gas cap side)

Questions:

1) Do PCMs have a history of going out? Does it usually take a few starts to clear the codes in a newly replaced PCM? (car runs fine with new PCM installed, but still shows codes 72, 22, 33).

2) How long do the timing chains typically last in these SCs?
 
Timing chains last until the motor gets rebuilt, at which time you usually replace it. in other words, I haven't seen anyone post that a timing chain has broken. The stock unit is plenty tough.

One way to trouble shoot if the IAC is causing high idle is to unplug it's connector and see if the engine dies. If so, either the IAC is shot or the engine computer is demanding the IAC to do something stupid.

If you disconnect the IAC and the engine will still run and idle, you have a big vac leak somewhere.

O.k.. so you did the PCM. why is he looking for vacuum leaks if the IAC is fine and the PCM fixed the problem? Makes me question if the PCM has fixed the issue.

72 isn't valid SC code. That refers to a MAP sensor. Our car has a BAP sensor.
22 is BAP sensor out of range. I've seen those sensors fail. I would clear codes, and then re-run the Key off and Key on tests.
33 is EGR valve not detected as opening. Does your car have EGR? Could be bad EGR valve. That gets a vacuum signal, maybe the vac line broke and there is your idle issue plus bad egr?

PCM's rarely fail but they certainly can. Usually what will kill them is a alternator going south in a bad way screwing up the electrical system and killing the computer. I've not heard of a SC EEC-IV dying, though I have one in my Ranger that is flakey as all get out. So it can happen.
 
New MAF didn't change anything, put my old one back in...swapped out IAC anyway (w/ new PCM), she runs like a champ. I saw the old PCM, there was definitely something fried internally.

So now it runs smoothly, but I have a hard "check engine light" on. Haven't had it come on in years (not counting starting the car), never came on when I had the initial high idle problem with my old PCM. Only code showing is 33. Mechanic showed me where the "DPFE?" (left front of engine/supercharger, near the top) was not connected to the EGR tube, which appeared welded to a small quarter size plate just below the DPFE. (Is this normal?) Said since it wasn't connected, I would get the check engine light and "33"...wouldn't impact performance or emissions.

True? What are some options to connect the EGR? Or is it something I can live with (minus staring at the check engine light)?
 
If there is a tube disconnected, that will be a problem. If it's just a connector, well connect it.

If it's a tube, it's going to leak something, either exhaust, or intake air.

No idea what a DPFE is. 33 is EGR Valve Opening not detected.
 
DPFE...PFE...EGR...I did a search and they seem to be related, just not sure how.

So what does a 89 SC have and if it is disconnected and I am getting a CE light w/ code 33, is performance affected? I can't find the EGR tube either, so there's nothing to connect to.
 
If your car does not have an EGR valve and the PCM you installed is programmed for one then you will get an EGR code.
 
I'll have to check on the EGR valve.

If I don't have a EGR valve, how easy is it to have the PCM re-programmed?

If I do, and it's not connected for some reason, any impact outside of a hard code 33 and CE light?

Thanks
 
If you have egr, and something isn't connected, one of three things are happening.

Control wire disconnected - no impact
Exhaust tube cracked - causes exhaust to leak into the engine bay, possibly pulled into the interior.
Intake tube leaking - causes a vacuum leak.

My guess is you don't have EGR (89's didn't have it did they?) and so you have a PCM looking for it. There may be a way to do something with the harness to get it faked out. I don't believe that the EEC will throw a strategy in due to the loss of input. But can't say for sure. If not, then there is no other impact other than the CEL light.
 
I don't know if this is 100% correct but I found it here.
89 EGR on both auto/5-speed
90 EGR on 5-speed only
90 auto no EGR
91 no EGR
92 no EGR
93 no EGR
94 EGR on both auto/5-speed
95 EGR on both auto/5-speed

Likley the EGR system is either bad or has been disconnected.
Check both the EGR vacuum and electrical connections.
You may have to pull of the cowl cover and more to get the full picture.
I know my 90 doesn't have one but the 95 does and it's a real pain in the neck to work on it.
 
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