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'84 Z24 suddenly won't idle


Kingman

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The pipe at the front is an air feed into the exhaust to burn off emissions in the cat. Normally between exhaust pulses there is a negative pressure or vacuum wave produced. That pipe was connected to a one way reed valve on the air filter that allowed gulps of air in. Has no effect on running.

 

The EGR pipe runs around the back of the head. As long as the EGR valve is disconnected it poses no problems. The EGR is this thing with the metal pipe going towards the exhaust.....

motorZ2022intakeEGRvalve.jpg

 

 

Hyspeedz, the most common problem with "not idling" is the idle-cut valve. If the alternator is not charging fully, if the red light on partially on, then it doesn't idle. Or the idle-cut valve has the wire disconnected.

 

 

Actually David that's the choke heater relay that does that when the alternator doesn't charge. The idle cut will work with or without charge.

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BlackCasio, the only thing visible in your photo is the BPT valve part of the EGR (on the top of the engine). It does nothing by itself.

 

 

When an engine won't idle under 1000 RPM, it is usually a vacuum leak. (By contrast if it idled only at 1500 RPM suspect the Idle-cut solenoid).

 

Vacuum leaks can occur everywhere:

 

Non-carb vacuum leaks

* broken hose ends

* Vacuum Advance

* Air Cleaner heat-flap motor (diaphragm)

* EGR Valve (newer engines)

* PCV valve sticking - causes part-throttle problems

 

Carburetor leaks

* choke vacuum break (or Weber DGEV/DGAV choke pull-off)

* Loose throttle shaft

* Loose base nuts. Do not overtighteen

* Loose adapter plate (Weber)

* Cracked adapter plate (Weber) - caused by overtightening

* Carburetor Dashpot (some engines)

* Throttle opener (some engines)

* Dashpot (some engines)

 

Use a $25 vacuum gun to test them:

14074.jpg

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Actually the EGR is disconnected. See the short hose with screw in it? It goes down to the top of the EGR and pushes on to the nipple just out of sight behind a hose. It's just above the metal pipe from the exhaust in this picture.

20121222_164701_zpsb80d04ca.jpg

 

Anyway the point is that the EGR is non functioning.

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It's a valve and deposits are crusty and can prevent them closing properly. As you know it doesn't take much of a leak on an intake to throw the idle off. Timers were installed on mid 70s cars and trucks to alert the owner to clean the EGR valves every 30K? or so..

 

EGR shouldn't affect performance if you define performance as full throttle all out power. EGR responds to a ported vacuum signal from the carb. Besides there being NO EGR when the motor is cold.... there is none at idle (so the EGR valve should be closed) and at full WOT the vacuum signal is low enough that there should be no EGR either. At all other part throttle positions EGR is metered by a vacuum signal and some later models by a vacuum signal modified in relation to exhaust back pressure.

 

EGR when added to the combustion chamber gasses lowers their peak temperatures below the point where nitrogen forms NOX. A by product of this is that less octane is needed and detonation reduced.

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You can easily test the EGR valve in place. There is no reason to remove and inspect it unless you are trying to get it smog tested.

 

To test an EGR valve, with engine cold at idle, reach into the valve and pull the diaphragm up with your finger, then let go. If the engine stumbles it is working correctly. If it makes no difference then it's not working. If it stumbles and dies and won't restart then yes, it probably needs a cleaning. Better to just leave it alone.

 

Working EGR does affect performance if you define it as normal driving performance. Only Wide-Open-Throttle and cold-engine performance is not affected.

 

The timer was for 50k miles. No inspection or cleaning needed before then.

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