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Discussion Starter · #1 ·
Hey i am just a beginner tech in school, but i got this car and its runnin real rich right now. The exhaust fumes are gas heavy. Idk much bout these old cars and i havnt tried much. It also has this long term intermittent issue where it stalls from a slow start or a stop n start. Happens maybe 1 time every month. Plus the idle once in a while drops to 400 rpms and the steering wheel will shake real bad. The regular idle is around 700 to 1k. The original owner had a similar issue and thought by setting that little screw by the throttle body to keep the throttle open slightly so that the rpms stayed at 1500 would solve it. He had it like that for several yrs. I just did some compression tests, spark tests and basic fuel tests to make sure all that was good a few months back and they were in the clear. So i dropped the idle back down to 700 and havnt had issues with it since. But it does still have a small tendency to drop to 400 and shake that wheel as stated earlier. Im not too sure what to look into since school doesnt teach us old car stuff any more.
 

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Check the vacuum lines between the engine and the MAP sensor. If it is like the Turbo models it will be on the front of the passenger side shock tower. Any cracks in them can cause what you are seeing.
 

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Discussion Starter · #4 ·
Check the vacuum lines between the engine and the MAP sensor. If it is like the Turbo models it will be on the front of the passenger side shock tower. Any cracks in them can cause what you are seeing.
Sounds good i ll check all these later after work. I feel like when i smoked the vacuume lines starting from the inlet of the brake booster vacuume line i would find most vaccuume leaks but they could have ripped in the past 3 months so ill do another smoke test
 

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1966 Crown Coupe, 2016 200 S AWD, 1962 Lark Daytona V8.
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Welcome to Allpar. There may not be any fault codes. That little screw on the throttle body is not an idle speed adjustment screw, it is a minimum air screw. They are adjusted and capped at the factory and should never require adjustment in the field. The idle speed is controlled by the PCM and IAC motor (it's basically a computer-controlled air leak into the intake manifold).

We have to diagnose and repair the root cause first. The previous owner didn't solve the problem, he compensated for it by adding air and may have added a second problem in doing so.
After the problem is found and repaired, there is a procedure with a special tool (orifice) to setting minimum air. You can't really do it by ear or RPM after it is tampered.

A DRB2 or an equivalent OBD1 scan tool with the Chrysler diagnostic cable would help, but you may be able to find the problem without a scan tool.
engine_connector_6-way_edit.jpg

Bosch or other aftermarket O2 sensors may cause mixture problems. Use OEM (NTK/NGK) or Mopar sensors.
Use the correct Champion RN12YC copper spark plugs, platinums may cause misfire, driving the mixture rich. The O2 sensor would see the high oxygen as a lean mixture and force the injector pulsewidth rich.

If the vehicle has an EGR valve, try unplugging the vacuum hose at the valve to see if the idle straightens out. There should be little or no EGR flow at idle. The vacuum transducer may have an internal defect if there is vacuum.
egr solenoid transducer.jpg

I did have a Neon with a rich idle and pulling the EGR hose made no difference. I eventually found out that it didn't make any diffence because the valve pintle had burnt off. It was getting full EGR whether the vacuum hose was on or off.
vacuum-controlled-EGR-valve-300x264-300x264.jpg
The EGR supply tube got hot a few seconds the engine was started (indicating exhaust gas flow) when there should have been little to no EGR flow. Don't burn yourself trying this.
s-l500.jpg
 
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Discussion Starter · #7 ·
Welcome to Allpar. There may not be any fault codes. That little screw on the throttle body is not an idle speed adjustment screw, it is a minimum air screw. They are adjusted and capped at the factory and should never require adjustment in the field. The idle speed is controlled by the PCM and IAC motor (it's basically a computer-controlled air leak into the intake manifold).

We have to diagnose and repair the root cause first. The previous owner didn't solve the problem, he compensated for it by adding air and may have added a second problem in doing so.
After the problem is found and repaired, there is a procedure with a special tool (orifice) to setting minimum air. You can't really do it by ear or RPM after it is tampered.

A DRB2 or an equivalent OBD1 scan tool with the Chrysler diagnostic cable would help, but you may be able to find the problem without a scan tool.
engine_connector_6-way_edit.jpg

Bosch or other aftermarket O2 sensors may cause mixture problems. Use OEM (NTK/NGK) or Mopar sensors.
Use the correct Champion RN12YC copper spark plugs, platinums may cause misfire, driving the mixture rich. The O2 sensor would see the high oxygen as a lean mixture and force the injector pulsewidth rich.

If the vehicle has an EGR valve, try unplugging the vacuum hose at the valve to see if the idle straightens out. There should be little or no EGR flow at idle. The vacuum transducer may have an internal defect if there is vacuum.
egr solenoid transducer.jpg

I did have a Neon with a rich idle and pulling the EGR hose made no difference. I eventually found out that it didn't make any diffence because the valve pintle had burnt off. It was getting full EGR whether the vacuum hose was on or off.
vacuum-controlled-EGR-valve-300x264-300x264.jpg
The EGR supply tube got hot a few seconds the engine was started (indicating exhaust gas flow) when there should have been little to no EGR flow. Don't burn yourself trying this.
s-l500.jpg
Alright this helps a ton and gives me alot to do. I did fully replace the egr valve just recently so i think i can cut that out of the equation but ill test it still just to confirm it. Idk much bout the screw thing however im guessing thats a big contributer to the issue ill loom more into that. Last time i checked spark plugs they were runnin hot would that be an issue for it (white coating around the metal). Yes you were correct there are no codes going off other whise id have already ran a check on that. I dont have easy access to obd 1 scanners rn or the money for it so its all gonna just be procedural manual testing throughout. What bout the carburator could that lead to a bad air and fuel mixture if anything i want to look into that as well. Sadly i have no knowledge of them. Thanks again for all this helps a ton with more to look into.
 

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What bout the carburator could that lead to a bad air and fuel mixture if anything i want to look into that as well. Sadly i have no knowledge of them.
An '89 would not have a carb. It's TBI (Throttle Body Injection).
 

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Discussion Starter · #10 ·
Welcome to Allpar. There may not be any fault codes. That little screw on the throttle body is not an idle speed adjustment screw, it is a minimum air screw. They are adjusted and capped at the factory and should never require adjustment in the field. The idle speed is controlled by the PCM and IAC motor (it's basically a computer-controlled air leak into the intake manifold).

We have to diagnose and repair the root cause first. The previous owner didn't solve the problem, he compensated for it by adding air and may have added a second problem in doing so.
After the problem is found and repaired, there is a procedure with a special tool (orifice) to setting minimum air. You can't really do it by ear or RPM after it is tampered.

A DRB2 or an equivalent OBD1 scan tool with the Chrysler diagnostic cable would help, but you may be able to find the problem without a scan tool.
engine_connector_6-way_edit.jpg

Bosch or other aftermarket O2 sensors may cause mixture problems. Use OEM (NTK/NGK) or Mopar sensors.
Use the correct Champion RN12YC copper spark plugs, platinums may cause misfire, driving the mixture rich. The O2 sensor would see the high oxygen as a lean mixture and force the injector pulsewidth rich.

If the vehicle has an EGR valve, try unplugging the vacuum hose at the valve to see if the idle straightens out. There should be little or no EGR flow at idle. The vacuum transducer may have an internal defect if there is vacuum.
egr solenoid transducer.jpg

I did have a Neon with a rich idle and pulling the EGR hose made no difference. I eventually found out that it didn't make any diffence because the valve pintle had burnt off. It was getting full EGR whether the vacuum hose was on or off.
vacuum-controlled-EGR-valve-300x264-300x264.jpg
The EGR supply tube got hot a few seconds the engine was started (indicating exhaust gas flow) when there should have been little to no EGR flow. Don't burn yourself trying this.
s-l500.jpg
Oh another weird thing i found. The day i replaced the egr valve (the old one was stuck open). That adjustment screw hadnt been touched yet and i noticed the avg rpm in drive was around 3500 after i replaced the valve. This was the only reason i decided to adjust that screw. As soon as i got the chance to adjust it and lower that idle its been fine since. However this was definately an odd occurance that i dont understand why replacing the egr valve would cause. Any clue on that?
 

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I always adjust the idle screw that's not an idle screw on my old cars to my desired idle speed.

For some strange reason, folks seem afraid to touch the forbidden screw.

Thanks
Randy.
 

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Discussion Starter · #12 ·
I always adjust the idle screw that's not an idle screw on my old cars to my desired idle speed.

For some strange reason, folks seem afraid to touch the forbidden screw.

Thanks
Randy.
Beats me man if it works it works. I just wanna make sure im doin it right
 

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In a perfect electronic world there is no reason to touch the forbidden screw.

What's right is what's right for you, I'm only sharing my experience.

Obviously it's different from some others by their warnings.

I have yet to hear a logical reason.

Thanks
Randy

Beats me man if it works it works. I just wanna make sure im doin it right
 

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In a perfect electronic world there is no reason to touch the forbidden screw.

What's right is what's right for you, I'm only sharing my experience.

Obviously it's different from some others by their warnings.

I have yet to hear a logical reason.

Thanks
Randy
That screw is to set the throttle blade so that it just barely doesn't stick closed. It's an anti stick stop. So, you can adjust it if that's how you adjust it. The ais is supposed to take over and bypass enough air to maintain the correct idle speed, not supposed to have air passing the throttle blade.
 
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Discussion Starter · #15 ·
Ill find the procedure to set it right but all in all i gotta keep lookin at other things. My next step is swappin the spark plugs and checkin for any vaccuum leaks.
 

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Oh another weird thing i found. The day i replaced the egr valve (the old one was stuck open). That adjustment screw hadnt been touched yet and i noticed the avg rpm in drive was around 3500 after i replaced the valve. This was the only reason i decided to adjust that screw. As soon as i got the chance to adjust it and lower that idle its been fine since. However this was definately an odd occurance that i dont understand why replacing the egr valve would cause. Any clue on that?
3500 sounds like a vacuum leak. I had one at a throttle body gasket, and it would jump over 2500 at idle, then in about 30 seconds it would slowly easy down. It cleared up when I fixed the leak.
White, blistered plugs are running too lean, which is the opposite of it being rich. But maybe you've had one condition and then the other.
 

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Discussion Starter · #17 ·
3500 sounds like a vacuum leak. I had one at a throttle body gasket, and it would jump over 2500 at idle, then in about 30 seconds it would slowly easy down. It cleared up when I fixed the leak.
White, blistered plugs are running too lean, which is the opposite of it being rich. But maybe you've had one condition and then the other.
Yeah well we shall see just gotta do further testing im still pretty clueless with it
 

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The leaking EGR would have acted like a vacuum leak, except with no (or little) oxygen and hot, inert exhaust gases that don't burn very well.

The min air screw is adjusted at the factory and then has a metal plug or cap installed to seal it. If that cap was missing, someone had already tampered with the adjustment.
 
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