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Discussion Starter #1
This is a 97 model Thunderbird with a 4.6 engine. Up until a few years ago I didn't have any of the following problems.

When in gear and stopped whenever I turn the steering wheel the idle speed drops way down and the whole car shakes.

On rare occasions the idle air control valve will make a wailing or moaning sound and the idle will get super choppy and usually die.

When cruising at a steady speed in 4th gear if I give it just a tiny bit of throttle I can just barely hear a little bit of knocking or detonating from the engine. A little more or less throttle will make it go away. Higher octane fuels don't seem to have any effect and I also pulled out the little computer chip on the right fender which affects the timing and that does seem to help reduce that knocking.

New plugs and wires seem to have no effect. I also tested the ignition coils and connectors and everything seems to be working properly in the ignition system.

I've also had the fuel injectors tested and ultrasonically cleaned then tested again and they all show to be working perfectly.

Recently I seem to be having some misfires on at least one cylinder which makes the car jerk under acceleration but it only does it when fully warmed up and between about 1500 and 2500 rpm.

In the past I suspected there was a vacuum leak so I tested all of the vacuum lines everywhere with a hand-held vacuum pump making sure there weren't any leaks anywhere and it all seems fine.

Does this sound like there's a problem with the ECM?
 

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Look for a vacuum leak toward the purge canister on the right side of the fender well. There is a metal line that comes from the throttle body, follow it down to where there's a rubber hose that connects the evap system. That hose usually rots after 10 years. Also check the ones going to all the components down there. I would also consider replacing that IAC and clean the mas sensor(i believe that's the little "computer chip" you referred to.)
 

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X2 on cleaning the MAF, which should eliminated the pinging. That is different from the timing spout that was removed. You should be able to put it back in after cleaning the MAF.

You will need a tamper proof torx bit to remove the MAF sensor (Autozone sells it), and electrical cleaner and a Q-tip to clean it. A magnifying glass is helpful also.

Al
 

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My car did not have quite the same symptoms but in my case the MAF & connector, IAC and connector, purge valve solenoid, purge valve sensor, and purge valve associated hoses were all replaced to resolve idle/stall issues.

You'd probably be well served replacing all vacuum lines anyway, it's a cheap and easy thing to do.
 

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Put a vacuum gauge on it, and see what it reads.

See if pressing the brakes changes it, and how it changes.

If the MAF hasn't been cleaned lately, you need to clean it.

If it's never been "Seafomed", search that and do it.

You'll be amazed how much that matters.

Change the oil and filter after a seafoaming; it washes a bunch of crap into it.
 

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Discussion Starter #6
Look for a vacuum leak toward the purge canister on the right side of the fender well. There is a metal line that comes from the throttle body, follow it down to where there's a rubber hose that connects the evap system. That hose usually rots after 10 years. Also check the ones going to all the components down there. I would also consider replacing that IAC and clean the mas sensor(i believe that's the little "computer chip" you referred to.)
I'm sorry for not responding earlier, but I didn't receive any notifications.

I did have a leak in the long vacuum line going to the charcoal canister a few years ago. The leak was in the metal line and i couldn't fix it, so I bypassed it and ran a new rubber line from the intake directly to the fender well. Plus I replaced all the short lines around the canister as well.

I've cleaned the MAF sensor on a regular basis.

The computer chip I'm referring to controls the spark advance. If the engine starts pinging, you pull the chip out and it's supposed to limit spark advance. I believe this was designed for situations where you get some bad gas.

I've considered replacing the IAC, but they are so expensive that I didn't want to do it unless I knew it was bad. I've removed it and cleaned it well a few times.
 

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Discussion Starter #7
X2 on cleaning the MAF, which should eliminated the pinging. That is different from the timing spout that was removed. You should be able to put it back in after cleaning the MAF.

You will need a tamper proof torx bit to remove the MAF sensor (Autozone sells it), and electrical cleaner and a Q-tip to clean it. A magnifying glass is helpful also.

Al
I'm a pro on cleaning the MAF. I can pop it off in less than 60 seconds. I also tend to pull the ecm fuse for an hour or so to reset the computer so it can relearn. This never seems to help my other issues.
 

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Discussion Starter #8
My car did not have quite the same symptoms but in my case the MAF & connector, IAC and connector, purge valve solenoid, purge valve sensor, and purge valve associated hoses were all replaced to resolve idle/stall issues.

You'd probably be well served replacing all vacuum lines anyway, it's a cheap and easy thing to do.
I've never gotten any codes for the MAF or IAC. Did you get any codes which led you to replacing them and their connectors?

Every couple of months I'll get a code for the purge valve, but I just turn the code off. I once temporarily plugged off the vacuum going to the purge solenoid to see if that fixed the idle or any other problems, but it had no effect at all.

All my vacuum lines have been checked, no leaks.
 

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Discussion Starter #9
Put a vacuum gauge on it, and see what it reads.

See if pressing the brakes changes it, and how it changes.

If the MAF hasn't been cleaned lately, you need to clean it.

If it's never been "Seafomed", search that and do it.

You'll be amazed how much that matters.

Change the oil and filter after a seafoaming; it washes a bunch of crap into it.
I have very high and steady vacuum, around 18", at idle. I checked the vacuum lines and check valve going to the booster and they are solid, no leaks.

Maybe there is a leak under the intake manifold? Maybe a crack? I'd like to get a smoke machine, but they are hard to locate.

I did a Seafoam cleaning a couple years ago and it had no effect. Since then I've used an actual fuel Injector cleaning device. You hook up a air compressor, set the air pressure to 20psi or so, fill the bottle with a cleaning solution, like lacquer thinner, pull the fuel pump fuse and basically let the engine run solely on the cleaner. I did two 15 minute sessions and it had no effect on the the engines problems.
 

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If you want to check the manifold for leaks you can take some carb cleaner and spray around it with the engine running and listen for the idle to increase if there's a leak. Some people say an unlit propane torch is safer and cleaner. Me, considering the time and effort already put into it, an IAC valve would not be an expensive alternative. You may want to pull it and check the gasket around it and try cleaning the valve. Also, the throttle body itself, my 96 got pretty gunked up at 100k.
 

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Discussion Starter #11
If you want to check the manifold for leaks you can take some carb cleaner and spray around it with the engine running and listen for the idle to increase if there's a leak. Some people say an unlit propane torch is safer and cleaner. Me, considering the time and effort already put into it, an IAC valve would not be an expensive alternative. You may want to pull it and check the gasket around it and try cleaning the valve. Also, the throttle body itself, my 96 got pretty gunked up at 100k.
I've tried checking the intake manifold gaskets for leaks with carb cleaner, and didn't find anything. I unplugged the IAC so I had a steady engine speed. When I talked about using a smoke machine it was to look for a crack underneath the manifold.

The last time I checked IAC prices they were $60+, but I see there are some cheaper units on the market from $30 to $40. That's not bad. Even though mine "works" it seems to react slowly, about a second too late. Like when the AC kicks on the idle drops too low for a second then it picks back up. It's annoying. I think I will get one and see what happens.

I'd like to confirm the ignition timing using a timing light and a rolling road to simulate it driving. It just seems like the computer is screwing things up on at least one cylinder.

Recently it's started bucking again under acceleration. I put all new plugs in just in case one of the old ones had a crack or something and no change. It's driving me crazy.

Maybe I could install a new crank position sensor. They are cheap at $10, but hard to swap out.
 

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Bucking under a load also could be a spark plug wire. If you decide to buy a IAC I would stick with Motorcraft. Check the online sites for a descent price. I've only had luck with Motorcraft or Autolite wires and plugs. These cars are not fond of cheap after market parts. I once put Champion double platinum plugs in my 96 and it started a lot of that crap after 5k miles.
 

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Discussion Starter #13
Bucking under a load also could be a spark plug wire. If you decide to buy a IAC I would stick with Motorcraft. Check the online sites for a descent price. I've only had luck with Motorcraft or Autolite wires and plugs. These cars are not fond of cheap after market parts. I once put Champion double platinum plugs in my 96 and it started a lot of that crap after 5k miles.
I recently installed new Motorcraft plug wires and Auto lite copper plugs and it had zero effect.

Let me see what the motorcraft version IAC costs.
 

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Discussion Starter #15
How did you test the coils?

D
You can take a digital multimeter and measure the coil resistances. The specs are in the manual. In addition you can pull each plug wire off while the engine is running. I got nice blue/white arcs over 1" long. That's very healthy.
 

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I don't think such tests exist.
:wink2:

Just making you think.

I've run into that with those old coil packs on both my own and customers cars. Also, fuel injectors cause some wonky stuff to happen even though they may have been cleaned.

But I'd replace that IAC first. if it's making a noise it's having an issue. Cleaning sometimes works, but usually not and often only short term if it does.

And be careful cleaning your MAF too often. You can damage it and not know it.

D
 

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Discussion Starter #19 (Edited)
I just installed a new IAC. Motorcraft was $57 online and $85 local. I didn't want to wait a week for a online one so I used my Oreilly's account and got the BWD brand for $45 plus tax.

Yes! It fixed one of my issues. It seems to respond very quickly to changes in engine load. When in gear and I turn the steering wheel the rpms don't drop way down making the car shake anymore. Even the AC cycling on and off seems smoother. I assume it won't make that weird moaning sound anymore either.

I don't know if it will fix any of my other problems, but I'll have to test it later and see. I know the idle is still a bit shaky. But overall, a well spent $50 indeed. :)
 

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I just installed a new IAC. Motorcraft was $57 online and $85 local. I didn't want to wait a week for a online one so I used my Oreilly's account and got the BWD brand for $45 plus tax.

Yes! It fixed one of my issues. It seems to respond very quickly to changes in engine load. When in gear and I turn the steering wheel the rpms don't drop way down making the car shake anymore. Even the AC cycling on and off seems smoother. I assume it won't make that weird moaning sound anymore either.

I don't know if it will fix any of my other problems, but I'll have to test it later and see. I know the idle is still a bit shaky. But overall, a well spent $50 indeed. :)
Go ahead and order the Motorcraft IAC and keep it. That aftermarket one won't last very long.
 
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