Surging Idle After Revving

Rosalio Avalos · Sep 24, 2016

Hello everybody, I'm currently having issues with my foxbody. When i let off of the gas after revving it. the idle will begin to surge. When i Rev it at high RPM's the engine will surge for a second and shutoff. After the engine has warmed up it will not start till it has cooled off again.
The Mods in the engine are as follows:

GT40 upper and lower intake
E303 cam
Stock e7 heads
Block bored 30 over
70MM TB and EGR spacer
BBK CAI
BBK shorty headers and full 2.25" exhaust

The timing is set to 14 degrees. I have an A9L ECM, im not exactly if my problem is with airflow/fuel, or if it has to do with the ECM. I've been considering a chip or a standalone tuner to support the mods.

mikestang63 · Sep 25, 2016

Run the codes. Could be a lot of things from a bad TPS, TFI, MAF, IAC, ECT, 10 pin connectors

a91what · Sep 25, 2016

+1 pull codes
don't bother with a mail order tuner, they all suck. trust me I have one sitting in the shed because they could never get the tune right [BAMA]... better off to go havethe car tuned by a shop but even then with your mod list the stock ecu should be able to compensate just fine.
The E303 cam is not friendly with EFI to begin with. I would check to see if the TPS is working correctly.

i now use a standalone ECU and will never go back.

jrichker · Sep 25, 2016

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.

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 200,000 hits, which indicates it does help fix idle problems quickly and inexpensively.

Rosalio Avalos · Sep 28, 2016

While going through the Surge/idle checklist i found a guy with an E-cam that had similar issues. According to him the IAC should be bored to increase the idle RPM. i messed with it a bit today, and it certainly did improve my surging issue. Thanks alot for your guy's inputs. hopefully i'll get it running soon, and i'll pull the codes to see what else i have to troubleshoot.

Gearbanger 101 · Sep 28, 2016

Don't go messing with anything before pulling your codes. You're spitballing until you do so. And you shouldn't be doing anything to the IAC but cleaning it.

stpete · Sep 28, 2016

I had to spend quite some time grinding my way through the checklist. Every time I found something, it helped but didn't fix the problem. I'm at the point now where the car runs pretty well. Still some surge with the AC on, but doesn't stall or hunt too much. I suspect I fixed the large vacuum leak, but still have one or more smaller leaks. You just have to work your way through. The first item of clearing codes and a basic tuneup was probably the biggest help. I think every piece on the list either had a problem or was on the verge in my car.
I also had an electric fan, stock alternator, and underdrive pulleys. The fan turning on while the car was idling would kill it. Dumb modifications can combine to screw you up also.

Rosalio Avalos · Sep 28, 2016

Is it possible to pull the codes with out being able to drive the car? It's been sitting for almost 6 months. I only connect the battery when I go to start it up.

jrichker · Sep 28, 2016

You can dump codes at any time, the car does not need to be driven. The computer stores codes for something like 82 engine off engine run cycles.

However, the computer loses stores codes and settings when the battery is disconnected. That may cause the engine to run rough or exhibit unusual behavior until it relearns the sensor settings and stabilizes. That may take up to 30 minutes of driving at a constant speed.

mikestang63 · Sep 28, 2016

Rosalio Avalos said:
Is it possible to pull the codes with out being able to drive the car? It's been sitting for almost 6 months. I only connect the battery when I go to start it up.

Yes, you can pull the stored or Key On Engine Off codes in addition to the car running that are Key on Engine Running codes... The downside is ovbviously the KOEO codes are not real time and will limit the results somewhat- it cannot tell you what is the state of the system now and what may be wrong when the motor is running and at operating temperature. If sensors etc have failed since the last time the motor ran, it may not pick it up. Also you will not be able to run a cylinder balance test. Can you at least get the car started and warmed up? then you can run all three tests- KOEO, KOER, and the cylinder balance test.

Surging Idle After Revving

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