TCCoA Forums banner

1 - 8 of 8 Posts

·
Registered
Joined
·
1,113 Posts
Discussion Starter #1
Hi everyone, I have a little problem. Not me, but the Cougar. Well, I do have problems... actually my problems have problems, but that is another story.

After I got my cats replaced and the car is running pretty normal, I found that I have an issue where the throttle is not dropping down after I let off the gas. While driving, and I need to let off the gas, the tac will show, let's say, 1200 RPM. It takes roughly about 3 seconds for the tac to drop down to normal and the car to start slowing down before I start using the throttle again. I hope that makes sense. Let me try another example. I am driving down the street at say, 59 mph. I need to slow down cause I am in a 45 mph zone and there is cop ahead. So I let off the gas, but the tac shows the idle is not dropping like any other car I have owned before. The Town Car, when I let off the gas, you can feel the car start to slow immediately (no tac to tell if the idle drops). Also, when the is car parked and idling, if I rev the engine, it takes about 3 seconds for the idle to drop.

Does the computer (EEC) control the idle in this manner? I put both a new IAC and TPS in last year along with just about everything else trying to figure out why the car had no acceleration (which turned out to be clogged cats).

Any suggestions would be appreciated.
 

·
Super Moderator
Joined
·
9,360 Posts
Yes, that's controlled by the PCM via the IAC valve. Despite it being newer I suspect it may be sticking. Might be worth cleaning (use something to work the valve open/closed as you flush it) to see if there's any improvement.
 

·
Registered
Joined
·
1,113 Posts
Discussion Starter #3
Hi Terminator,
I considered that but what keeps eating at me is the PCM / EEC was damaged in a car wreck before I bought it. It may not have sustained internal damage, but the casing was pressed / smashed to expose the insides. Over 25 years, I have to wonder if the elements would have effected the units ability to "think clearly" so to speak.

I will put the old IAC in this weekend and see if it changes anything.

Thanks!
 

·
Super Moderator
Joined
·
10,758 Posts
Make certain the engine mount on the driver's side is good; I had an issue like that, and it was the engine rising up and hitting the hood, causing the TB butterfly to open.

Look for a torn/indented patch in the hood liner. :)

I broke 3 wheels finding that out. :D
 

·
Registered
Joined
·
1,113 Posts
Discussion Starter #5
Funny you mention that. I had to replace the engine mounts a while after I bought the car. That was some 20 years ago and it could be the issue. I have to get the car up on jacks this weekend and fix an exhaust leak at the drivers side manifold and replace the mufflers. Good time to check the mounts. I looked at the hood liner last week when checking the oil and did not notice anything unusual, but who knows.

Thanks Grog!
 

·
Registered
Joined
·
1,113 Posts
Discussion Starter #6
UPDATE: I put the old Motorcraft TPS back in and the idle drop issue still persists. The car idle does not drop for about 3 seconds when you let off the gas.

Is the PCM the issue since replacing the TPS did not make a difference?

On the other note about Grogs suggestion of the engine mounts, they are in good condition and the hood fire block pad is in very good condition, no engine lift when the engine is revved. I did have a bolt coming lose on the exhaust manifold to the cat and this time used sealant and tightened it all up. On the new mufflers, I am waiting for the lap joint clamps to come tomorrow. Nobody had the size I wanted so I had to order them from Amazon. Kind of baffles me that the exhaust OD size is 2" but the new muffler ID is 2 3/8" That is a heck of a cap. I bought two, 2" ID to 2 1/4" OD sleeves to help tighten up the gaps between the exhaust pipe and the new muffler. I will take some pics.

Any suggestions on the idle issue would be appreciated.
 

·
Super Moderator
Joined
·
10,758 Posts
When you replaced the TPS, did you clean the Throttle body and butterfly area?

There's crud that builds up on the backside of the blade, and causes weird off-idle transition problems; I guess it could hang an idle as well.

I usually pull the TB off to clean it, but spraying it and wiping it with a rag carefully can do the same thing.

I don't recommend washing all the black crud down into the intake, lol.

I know in the 98 TB I have, there are some tiny passages that seem idle related; those may be clogged.
 

·
Registered
Joined
·
1,113 Posts
Discussion Starter #8
Thanks Grog, that is a good point. But I had just cleaned the intake, replaced all the parts, etc so there should not be any grime in there and all I saw was clean, clean, clean.

The more I thought about this while testing my new mufflers on a drive, I realized the hesitating throttle drop has always been an issue with this car since I have owned it. I am going to look for a replacement PCM / ECM since that is the last part of the puzzle and as mentioned is physically damaged with a smashed case. The issue is probably weather related since it has popped open for some 20 years, exposed to water, moisture, etc.

On a lighter note, I used to have a lag or hesitation when I would rev the engine. It also had hesitation during take off. If anyone would have told me to replace my exhaust system, I would have thought they were nuts. Well, after new cats, no resonator and new mufflers, the car actually has pickup, takes off and an I can REV THE ENGINE NOW. OMG... something so stupid.

When I was looking to replace the exhaust years ago, and asking if removing the resonator would help, one of the members replied "it may help some, but if its the wife's car, she won't be happy." I don't know about the happy part yet, she has not been in the car since I got the new mufflers in, but the low bass rumble is quite noticeable. If she says anything, I am getting the dual pipe system on ebay made for the T Bird / Cougar and I use the two resonators I have laying around that are new.

Thanks everyone for the feedback, it is always appreciated. I hope my updates and conclusions / experiences with the work I have done on this car has helped others with similar problems.

When you replaced the TPS, did you clean the Throttle body and butterfly area?

There's crud that builds up on the backside of the blade, and causes weird off-idle transition problems; I guess it could hang an idle as well.

I usually pull the TB off to clean it, but spraying it and wiping it with a rag carefully can do the same thing.

I don't recommend washing all the black crud down into the intake, lol.

I know in the 98 TB I have, there are some tiny passages that seem idle related; those may be clogged.
 
1 - 8 of 8 Posts
Top