Engine Inconsistent idle and excessive vibration.

Window

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Feb 13, 2017
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1989 lx 5.0. Just installed new edelbrock performer upper and lower intake, 19 lb injectors, 65mm egr spacer and throttle body. I didnt set my timing with a light, i took a picture before i pulled the distributor and put it back how it was. Maybe this is my issue. The car starts and idles its just not steady idle, sits at 800 and falls to 700 then goes back to 8 in like 5 second cycles. When it starts to fall it causes the whole car to shake then it goes back up and the shake goes away. Rinse repeat. I had it running for what seemed to be about 10-15 mins with no issues then this. So idk if its timing or what. The gas was sitting for a little over 6 months. I check it and it looked fine, i also put 2 gallons with some fuel system cleaner on top of what was in the tank. Any ideas?
 
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Dan02gt

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You're going to have to use a light to set the timing. Even a few degrees of rotation off can make a big difference. I also suspect you have a vacuum leak somewhere. Go over the vacuum lines really good. You may even want to spray something like starting fluid around the gaskets to make sure one of them didn't slip during the installation.
 

Mstng93SSP

You have a nice rear end there Dave.
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I agree with you need to set with a timing light. For now you can try turning your distributor slightly left and right and see if the idle smoothes out but make sure you get a timing light on there at some point.
 

Window

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ive tried turning it by hand and it doesnt seem to change much unless i go a lot, like a quarter turn. it was running and idling fine for like 10 mins. maybe once it got up to temp something changed. safe to say running cold it was okay. i have not driven it yet because i need to adjust the holes on the throttle cable bracket because of valve cover clearance. maybe once i open it up and run it things might change. i wont know until tomorrow when i can fab the bracket at work. the motor stays on it just doesnt feel right. ill also get a light and do that the proper way i just wanted to start it today, but i almost want to rule it out because it idled fine for a little while. im no professional as you guys can tell kinda learning as i go.
 

Mustang5L5

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Set timing to 10 degrees.

Check TPS and verify it is between 0.6 and 1.1 volts.

Perform Idle reset procedure to allow engine to relearn proper idle strategy.

Pull codes, and address any faults that come up.
 
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Window

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Im gonna be doing the timing with the light and i was told that setting the timing to 14 instead of 10 and using 93 octane might fetch more power. Can anyone confirm this? Stock 302 block with minor bolt on upgrades.65mm tb and egr spacer edelbrock performer intake with smog and ac delete. Also i always put 93 because i felt the car ran better than on 87. Im probably reaching here.
 

Mustang5L5

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For the sake of troubleshooting, set timing to base 10 degrees. Later on when you've sorted things out, you can bump to 14 degrees. You will require 93 octane for that.
 
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Window

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Well all is good, took a couple trys to get it perfect but i drove it up the road no knocking or pinging. Only thing is the idle is a little low around 500, i can fix that with the adjust screw on the tb right?
 

jrichker

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You guys with idle/stall problems could save a lot of time chasing your tails if you would go through the Surging Idle Checklist. Over 50 different people contributed information to it. The first two posts have all the fixes, and steps through the how to find and fix your idle problems without spending a lot of time and money. It includes how to dump the computer codes quickly and simply as one of the first steps. I continue to update it as more people post fixes or ask questions. You can post questions to that sticky and have your name and idle problem recognized. The guys with original problems and fixes get their posts added to the main fix. :D

It's free, I don't get anything for the use of it except knowing I helped a fellow Mustang enthusiast with his car. At last check, it had more than 250,000 hits, which indicates it does help fix idle problems quickly and inexpensively.
 

Mustang5L5

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The ECU should be controlling the idle with th E IAC and bumping it up a tad. Did you perform the idle reset by unplugging the IAC, setting idle and then resetting the ECU?
 
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Window

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What you said was right mustang5L5. I was so fixated on the timing last night i negelected the iab all together. Just did the proper procedure and reset ecu and it runs perfect now. Thanks everyone for your knowledge.
 
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Window

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i read somewhere that i should let the car sit for a day or two to let the procedure really take to the ecu. is that a thing?
 
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