‘95 80s has an extremely rough idle. What can I do? (1 Viewer)

Joined
Nov 29, 2020
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17
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Charleston- SC
Recently, my cruiser has been idling very rough. It will stay around 700 RPM, and then suddenly drop to about 200 RPM and nearly stall. Has anyone had trouble with this before? What do I do?
 
Joined
Aug 8, 2018
Messages
667
Location
Lake Waconia, MN
Just to start:

Be sure battery terminals are tight.

Check the main air intake tube from the air filter to the throttle body. They tend to crack at this age and create all sorts of issues. Very common and easy to check.

Looks like this:

Amazon product
Look for any major vacuum leaks - did a hose pop off the top of the engine or throttle body?
 
Joined
Apr 27, 2011
Messages
413
Location
Arkansas
If your battery terminals are clean and tight and your satisfied you don't have vacuum leaks it is possible the fuel pump relay points are worn. New FP Relay and save the old for a spare is the best bet but you can burnish the points on the relay as well. There are threads on this in this forum.

 
Joined
Nov 29, 2020
Messages
17
Location
Charleston- SC
Just to start:

Be sure battery terminals are tight.

Check the main air intake tube from the air filter to the throttle body. They tend to crack at this age and create all sorts of issues. Very common and easy to check.

Looks like this:

Amazon product
Look for any major vacuum leaks - did a hose pop off the top of the engine or throttle body?
Just checked and there seems to be no indication of a vacuum leak. I don’t know if it will help, but there is a very strong gasoline smell that comes from the exhaust and a little bit from the engine bay when the motor is running.
 
Joined
Nov 29, 2020
Messages
17
Location
Charleston- SC
If your battery terminals are clean and tight and your satisfied you don't have vacuum leaks it is possible the fuel pump relay points are worn. New FP Relay and save the old for a spare is the best bet but you can burnish the points on the relay as well. There are threads on this in this forum.

Thanks for that, will definitely give it a try the next opportunity I get.
 
Joined
Dec 10, 2007
Messages
7,506
Ditto: Does the engine do this all the time, rarely, every five minutes, only when cold, or only hot, or??

Did you do anything different before the symptoms began; washed the engine, driven through deep water, fiddled with anythng under the hood, get gasoline at a new station, --- ??
 
Joined
Nov 29, 2020
Messages
17
Location
Charleston- SC
Ditto: Does the engine do this all the time, rarely, every five minutes, only when cold, or only hot, or??

Did you do anything different before the symptoms began; washed the engine, driven through deep water, fiddled with anythng under the hood, get gasoline at a new station, --- ??
The engine does this all the time every 5 minutes or so. I changed the oil awhile back, maybe 300 miles ago. As for deep water, not really, I hit a big puddle every now and again since it’s been raining a lot lately. As for under the hood, I recently replaced the starter as it was going bad.
 
Joined
Dec 10, 2007
Messages
7,506
Does it run rough when you first start a cold engine, or only after it warms up and after the idle comes down?
 
Joined
Jun 22, 2018
Messages
101
Location
Houston, TX
I had the exact same issue, went through all the FSM checks and finally found the egr valve was stuck In the open position.

An easy test is to remove both vacuum lines at the top tee fitting coming off the valve shown in the photo. Place a finger on one side, and use an air nozzle to get 10-15psi on the other inlet. If it is a stuck valve, this will force it closed, and the rough idle will go away immediately.

3F0DE33C-D95A-4BCD-AF85-DF7457BD8967.jpeg
delete threads are a good option if this is the case.
 
Joined
Nov 29, 2020
Messages
17
Location
Charleston- SC
I had the exact same issue, went through all the FSM checks and finally found the egr valve was stuck In the open position.

An easy test is to remove both vacuum lines at the top tee fitting coming off the valve shown in the photo. Place a finger on one side, and use an air nozzle to get 10-15psi on the other inlet. If it is a stuck valve, this will force it closed, and the rough idle will go away immediately.

View attachment 2512280 delete threads are a good option if this is the case.
Will certainly give this a shot when I get a weekend. currently working 7/12’s, hardly any time to work on it at all.
 
Joined
May 3, 2016
Messages
1,036
Location
odessa, tx
This could be so many things. As one person suggested it could be your EGR. Depending on where you live you can delete it. It could be a bad injector, your injector harness. I would start with looking for vacuum leaks. You mentioned a gas smell under the hood. This is probably due to your charcoal cannister. It probably needs replacement. Additionally there is a vacuum line that comes off of it and runs under the intake to a web of lines, switches and valves. I would look into testing and replacing those after checking everything else. The easiest way to replace all of that is to pull your upper intake. Before that, Pull the idle air control valve and clean it. Pull the throttle body and clean it. Don't mess with the VAF. A simple thing to check that is often over looked is your AC system charge. If it is over charged it will run roughly as the compressor continuously kicks on and off. Have you added any refrigerant to the system lately?? It could be your fuel filter, fuel pump, fuel pressure regulator. Spark plugs, distributor or wires. In short it could be anything that affects spark, fuel and air. You will have to go through and start eliminating culprits.
 

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