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quick35th
04-04-2004, 04:19 PM
My 91 SC vibrates a little when it is put in drive or reverse. It goes away as soon as I give it gas. When it is in either drive or reverse it idles around 500rpm, and when it is first put into gear it sometimes drops below 500rpm and comes back up. Could it be my IAC or is it tranny related?

Also sometimes the tranny shifts hard into OD and has 163K on it.

Thanks!
Shane

cougarsc
04-04-2004, 04:28 PM
CHeck engine mounts. Also could be a torque converter shutter.

quick35th
04-04-2004, 05:15 PM
The engine doesn't shake at idle at all. I just changed the oil in it last night and looked at the motor mounts. I am no expert with them but I can discribe what I saw. They looked intact and the black paint or whatever it is on the outside was pealing off of both of them.

Any ideas?
Shane

SlinginBeauty
04-04-2004, 06:53 PM
hey quick35th, i seem to have the same problems going with my tbird. Im not to sure what it could be. I do know that i replaced the Harmonic Balancer and the Tranny and It seemed to be cool b/f all those. I also put in a dual ic. Ive been thinkin it maybe some kind of vacume seal with the ic but im not sure on that one. It idles fine in P but when you put it in d or r it drops idle and starts a vibration that i to can feel through the stearing wheel somewhat. Ive done some research and was thinkin it maybe my IAC. Havent checked that. Also, lots seem to blame a similar problem on broken motor mounts, even though i dont know how that may cause this vibration. So my thinkin its a vacume leak, bad IAC or maybe a mount. Need to put some more effort towards diagnosting my problem but when i saw this its the same thing so i though would add my .02. What mods have you done latly? When did it start vibrating? After a certain mod? or has it been that way for a while and your not to sure? I want to figure this out b/c its kindof lame sitting at idle in d and having it sound like its going to cutout or somethin. Its a terrible idle. Maybe i need a chip??? Thanks for all help. Zach

quick35th
04-04-2004, 11:57 PM
Zach, I just bought my 91 SC on the 29th, and it was like that when I took it for a test drive. I just figured it wasn't that big of a deal and delt with it. It is bone stcok too with 163K. All my mods are on the 35th.

The gauge reads good vac so I dont think it is that and the motor doesn't shake at all so I dont think it is the mounts. The one thing that I can think of would be the IAC. I have a brand new Ford IAC on my 35th so I could sometime this week swap them to see what difference it makes.

Also as of lately the vibrations seem to be getting better so I am leaning toward the IAC but wont know till I try it.

Thanks!
Shane

SlinginBeauty
04-05-2004, 12:03 AM
can you let me know how those test come out. Thats what i was figuring too with the different readings ive been getting. Hasnt been a constant thing, sometimes worse than others and really what i was leaning towards. Thanks for your help. Zach

trife86
04-05-2004, 01:37 AM
i have that same problem, i replaced the IAC that wasnt it, everything else you guys tried i also tried. i just cant figure it out it runs great but holds a very low idle. motor mounts are about a month old

tsc92
04-05-2004, 05:12 AM
Just a suggestion, keep your fluids filled correctly in trans, engine, supercharger. When is the last time you checked the supercharger fluids?

But you said, symptoms are rough idle when its in gear, and sometimes a hard shift into higher gears. I would say the rough idle is simply a tune up job. Some ajustments to the throttle position, or check the vaccum hoses for leaks (it sould be at 15-20 Hg at idle). Disconnect the Mass Air Sensor to see if it runs better without the senor. If disconnecting a sensor makes the car run better, without the sensor... the sensor is defective.

And you can run a self diagnostics test on the car with a voltometer, and read the error codes which will pinpoint the point where the system is failing. Reffer to the Hayes Repair Guide 'Error Codes', in the Emmissions & Exhaust System Section. There are a set of plugs on the passenger side, all the way in the back...you use those plugs to run Self Diagnostics Tests.

Good Luck
-Mike N

quick35th
04-05-2004, 09:14 AM
Well I'm going to have someone put the car in gear wile I unplug the IAC and I will see if that helps.

Also, this morning when I went out to start her it wouldn't start. It just kept turning over. At about the third attempt to try to start it it finally caught, so it is the IAC or maybe the cam sensor is starting to go.

Shane

quick35th
04-05-2004, 09:17 AM
i have that same problem, i replaced the IAC that wasnt it, everything else you guys tried i also tried. i just cant figure it out it runs great but holds a very low idle. motor mounts are about a month old

Where did you get your IAC at? If you got it at an auto parts store that could be your problem. I read on here once that the IAC has to be replaced with a Ford unit as the parts store's units are backwards inside.

Shane

TbirdSCFan
04-05-2004, 09:37 AM
I've sort of watched this thread go on for a bit, thinking someone would respond with advice on how to check your engine mounts. But that hasn't happened, so I'll ask how you determined that your engine mounts were OK.

Do a search on engine or motor mounts and see what the discussions tell you.
Your problem description is consistent with failed engine mounts. If you are experiencing a low idle as well.. there's your problem.
Good luck. :cool:

SlinginBeauty
04-05-2004, 10:05 AM
See, i knew everything that would comeup. lol. I havnt checked motor mounts and i have heard thats a common place to start. I was thinkin closer to the iac since it is iratic and sometimes my vacum stays 18-19 and others at idle it drops down to 13ish. Was thinkin it maybe a vacume leak to but ive checked and it doesnt always drop down to 13ish. Also with leaks ive noticed if i was at 13inhg and started acc the vac would go to 18and then back down till i get boost going. It feels like air or something. Ive done plenty of searches and like i have said they all come back with same problems, different areas to look and noone ever said they really fixed the pro. It seems that alot of us are suffering from a similar problem and i would love to get it fixed. Ill wait to see how the new IAC helps out but sounds like it maynot be the pro. Hopefully we will get this pinpointed down soon and get our babies running nice like they should be, lol. Thanks all for imput as it is all appreciated. Zach

SlinginBeauty
04-05-2004, 10:07 AM
See, i knew everything that would comeup. lol. I havnt checked motor mounts and i have heard thats a common place to start. I was thinkin closer to the iac since it is iratic and sometimes my vacum stays 18-19 and others at idle it drops down to 13ish. Was thinkin it maybe a vacume leak to but ive checked and it doesnt always drop down to 13ish. Also with leaks ive noticed if i was at 13inhg and started acc the vac would go to 18and then back down till i get boost going. It feels like air or something. Ive done plenty of searches and like i have said they all come back with same problems, different areas to look and noone ever said they really fixed the pro. It seems that alot of us are suffering from a similar problem and i would love to get it fixed. Ill wait to see how the new IAC helps out but sounds like it maynot be the pro. Hopefully we will get this pinpointed down soon and get our babies running nice like they should be, lol. Thanks all for imput as it is all appreciated. Zach
Oh and P.S. I have changed all my fluids in the last 3 months and they are all clean. I go to high expences to make sure my car gets what she wants and only the best. The one thing that i havnt check is the sc fluid. Ill check that this morning but as its a relativly new sc i dont think thats the pro. Ill keep you all posted.

lgarner
04-05-2004, 11:04 AM
The idle will naturally drop when going from Park to Drive or Reverse. If your motor mounts are shot you will feel a vibration throught the whole car. Also, hard shifts (especially from 1st to 2nd) are another side effect of broken motor mounts. I just did mine this weekend and it fixed all these problems.

Regards,
Lee

quick35th
04-05-2004, 10:41 PM
I'll have to read up on how to check for bad mounts.

The IAC is not the problem on my car. I had a friend put the car in gear wile I unplugged the IAC and the rpm dropped to 250.

So that leaves the motor mounts next to look at.

Thanks!
Shane

SlinginBeauty
04-05-2004, 11:38 PM
I will check mounts tomorrow and see whats happeing. I also emailed previous owner about their situation b/c he "rebuilt" the engine. lol. Still ive had every pro in the book and in the end i too will be an sc expert. Put that aside i came up with an question. How would the bad mounts only really affect when its in gear at idle. I can understand idle but why would it change and get worse when you put it in gear. I know your rpms's drop when you do put it in gear but dont see why that could make it only happen in gear. Wouldnt it happen in park too? i guess maybe it may but then again its late and i havent noticed the funny idle in park. so info??? Just giving ideas. Hope we all get this figured out. How do i go about checkin my iac? i may try that and see if that is my problem. All info is appreciated. Zach

TbirdSCFan
04-06-2004, 09:39 AM
... How would the bad mounts only really affect when its in gear at idle.... AFAIK, when its in gear, the engine is under a slight load and develops some amount of torque. This is what pushes the pass side limiter arm into the bracket and allows the vibration through the frame. When you rev the engine up, the harmonics settle out, so you don't notice it.

...Hope we all get this figured out. How do i go about checkin my iac? i may try that and see if that is my problem. All info is appreciated. Zach As far as the IAC, start the car, unplug it.. if the engine stumbles and dies, the IAC is good.
I'm sure you're wondering how bad mounts can cause this problem, aren't you.. as silly as it all sounds. But its not really, the problem is very common with the SC. It has to do with the fluid filled mounts that collapse with age and allow metal to contact metal. The vibrations get picked up by the knock sensor and the EEC retards the timing to adjust for it, hence the low idle. :cool:

SlinginBeauty
04-06-2004, 09:46 AM
Thanks for the responce. I just got an email back from previous owner and to his knowledge they are stock mounts :eek: Ill get down and check them out today. Your explanation makes perfect sense. Thanks for the help and ill post back with my info. Really appreciated. Zach

SlinginBeauty
04-06-2004, 12:14 PM
I havent gotten under to check my mounts yet but if i shake the ic pipe the engine does not wobble like i have seen someone say it should. My mounts may be bad but i didconected my IAC and the car kept idle, pro better than it normally does. Does this mean its the IAC on my car? Its suppose to stumble and die but it seemed better off with it unpluged than it did with it pluged in. So??? All help and info is appreciated. Thanks. Zach

TbirdSCFan
04-06-2004, 01:03 PM
Interesting that it idled. I wonder if a warm engine makes any difference. I 'm going to have to try this myself. There might be a problem with the IAC.. maybe you should leave it unplugged until you get a chance to inspect the mounts. You can try to take it off and clean it just dont touch the bellows part with anything, not even your finger. It can rupture, and then your idle will do the opposite and race. Spray some carb cleaner or brake cleaner in the body and swish it around and drain.

As fars as the mounts again, worn mounts can cause worse problems if left alone, so I definitly think they should be inspected. The oil pan and/or the power steering hose can crack :eek: Easiest way is to crawl under with a flashlight and look up from the back side of the engine. If the limiter arms (flat looking things poking through a square hole) are resting on the frame, the mounts are shot.