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Discussion Starter #1
Alright, so my friend has a 1995 Mark VIII that she hasn't been running lately because it idles so fast. She told me it was idling anywhere from 3500-4000 rpm and was simply impossible to drive like that (I can imagine!)

So I told her I would look at it. She had already had a few people look at it and she had bought a new IAC valve. Well, being a gen1 4.6L 32v, what a PITA that was to change, but I changed it. While I was there, I found the rubber vacuum T was totally fubar and another vacuum line was disconnected. I fixed all those problems and put it all back together.

Well, now it idles ~1500 which I found disappointing. She said it's always idled that fast since she's owned it. I told her that was NOT normal, it should idle around 700. Anybody got any ideas what I should look for? I unhooked the rubber T from the vacuum port on the throttle body and plugged the port, but it didn't help, so no vacuum leak in that sub-system. Could a TPS be the culprit? I was gonna test that next.

Please help me out, y'all. Master486? I know you'll have some ideas! BTW, is the 1995 Mark 8 DOHC OBD-II; I was thinking not because I saw the EEC test port under the hood.
 

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Discussion Starter #3
Why was an IAC valve hard to replace on the 32v 4.6? maybe it's better on 97-98 cars, but it look me like 30 seconds.

I'm pretty sure the 95 is OBD-I
Yes, the 97-98 are GEN2 32v engines (the moved the IAC to a more accessible location) and MUCH easier to get to... I'm happy for you. j/k :)
 

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Discussion Starter #7
my 95 is OBD2 check the emissions label, clean the MAF?
Yeh, my '95 'Bird 4.6L is OBD-II as well, but the Mark VIII did not get OBD-II until 1996 I've found/figured out. I've already listened and looked for any vacuum leaks, but will give it the "carb cleaner" test for that tomorrow. I'm almost positive it's the TPS, I've got the TSB describing how to test the OBD-I TPS used on these cars and will be checking that tomorrow morning as well.

As for the MAF, it doesn't even have one that I could see and I had it all apart this morning. The TPS is supposed to be .65-1.26v at idle according to reference TSB 94-26-4 Figure 2 - 1995 Mark VIII, which is applicable I believe.

GM, I just put a brand new IAC valve on this morning and it lowered the RPM's some (or it could have been the two vacuum leaks I fixed) - see post #1, and the one I took off looked pretty new like someone just changed it not too long ago.
 

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its either a vacuum leak or the iac valve
Usually after I fix my obvious vac leaks on a 4.6 sohc or 4.6 dohc with high idle problems I unplug the iac if it stumbles out and dies I change the valve. If it stays running at normal idle I continue my leak search. I know it's not scientific but it has always worked for me in the past. I actually just did this today on my own bird, it had an iac problem another way is I usually can hear a howling or whining coming from the defective iac on decel.
 

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Usually after I fix my obvious vac leaks on a 4.6 sohc or 4.6 dohc with high idle problems I unplug the iac if it stumbles out and dies I change the valve. If it stays running at normal idle I continue my leak search. I know it's not scientific but it has always worked for me in the past. I actually just did this today on my own bird, it had an iac problem another way is I usually can hear a howling or whining coming from the defective iac on decel.
You have it backwards. If you unplug the IAC while the car is running and it stumbles and dies, that means the IAC is working properly. If it continues to run after unplugging it then the IAC is stuck.
 

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Discussion Starter #12
then hook up a scanner so you can look at the short & long term fuel trims...if they are off, then that automatically implies vacuum leak(s)...also, the maf should be within the airbox assembly in the marks
Yeh, I remember seeing it now that you mention the air box. I unhooked the air tube and I remember seeing the little metering tube when I looked down the airbox hole *doh!* lol... Thanks, GM.

There is no vacuum line leaking for sure, I checked all that. I didn't get over there today cause I had other jobs to do, but I will spray looking for mating surface and other leaks before I get a new TPS. I just have a real good feeling the TPS is what is wrong.

Idling at 4K?!? That's just something I don't come across every day, and like I said in post #1, I fixed two vac leaks and replaced the IAC. Now it idles at 1500, which is MUCH better, but still not right...

I'll keep y'all informed of my progress! Have a good week-end everybody. Tomorrow scallop season starts here and our little town is packed. FWC moved it up cause of the oil spill and they also granted this weekend "free recreational salwater fishing", so no license required! All other laws apply.
 
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