2000 Mustang GT surging idle/cruising

Snow White 2v

New Member
May 12, 2019
4
0
1
19
Wichita, Kansas
My car is having a very strange idling issue.

When you first start it up for the first maybe 10 seconds it idles consistently. After that it’s like it’s got a Bluetooth cam you can turn on and off that lopes to the moon. In essence, it surges from 400-1000 RPMS periodically. Every now and then it’ll balance out and idle consistently, then boom, it’s cammed again.

Whenever I’m cruising with light throttle input it’ll surge and buck no matter the gear/rpms. Occasionally it will become so bad that it’s almost like it’s building up pressure when initially lifting off the pedal. Push down on the pedal and it feels like it keeps building pressure till it finally sputters, clears its throat, and lurches.

What confuses me the most, is the car performs fine under full throttle in the rpms, if not flawlessly. If you’re cruising but slowing applying throttle it’ll feel somewhat sluggish and then once the pedal is matted it feels like it clears its throat and goes.

I’m pretty stuck!! Any help is GREATLY appreciated!

codes I’ve gotten: p0401 (EGR insufficient flow) and p1152 (rich)

I’ve replaced the EGR valve and DPFE, replaced the pcv valve, cleaned throttle body and intake plenum.

Mods
SCT X4 91 canned tune
Edlebrock victor jr intake manifold
BBK 78mm TB
Fender CAI
LTH
 
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08GT500

Active Member
Jul 12, 2018
898
139
53
50
Massachusetts
Hi,
What year, exactly is this, and did this issue start with any recent changes made? Much easier to help with specifics.More cold engine occurrence than hot?
Your canned tune isn’t helping anything, should get a custom tune-but as for the intermittent problem.
Have any more codes(or have you checked for ones in the absence of a CEL) since you replaced your EGR? Can you run a data log with your OBD-2 Scantool? If so- Drive it & catch the data for a more accurate response as to what’s occurring.
Run it through the PID’s and look for an O2 sensor that’s pegging & not correcting, as well as your fuel trim. Note the changes that occur when this happens.
Check all your grounds, Battery to block, block to Chassis, Battery to EEC.
1) Have you checked your TPS, it’s output voltage?
2) You’d mentioned cleaning things up, did you clean your MAF with CRC MAF cleaner?
3) It May very well be a plug wire arc, or a fouled plug, Fire the car off in the dark & look for stray arc’s. Check your cap for a crack, rotor, wire routing near headers, etc, & your electrical connections.
4) Check your IACV for proper function & no air leaks. Do a once over on all vacuum lines, replace any questionable’s.
5) Coolant level check & verify function of your Engine CTS.
Good luck!
-John
 

light-em-up

Member
Feb 25, 2020
6
2
13
61
Midwest
My car is having a very strange idling issue.

When you first start it up for the first maybe 10 seconds it idles consistently. After that it’s like it’s got a Bluetooth cam you can turn on and off that lopes to the moon. In essence, it surges from 400-1000 RPMS periodically. Every now and then it’ll balance out and idle consistently, then boom, it’s cammed again.

Whenever I’m cruising with light throttle input it’ll surge and buck no matter the gear/rpms. Occasionally it will become so bad that it’s almost like it’s building up pressure when initially lifting off the pedal. Push down on the pedal and it feels like it keeps building pressure till it finally sputters, clears its throat, and lurches.

What confuses me the most, is the car performs fine under full throttle in the rpms, if not flawlessly. If you’re cruising but slowing applying throttle it’ll feel somewhat sluggish and then once the pedal is matted it feels like it clears its throat and goes.

I’m pretty stuck!! Any help is GREATLY appreciated!

codes I’ve gotten: p0401 (EGR insufficient flow) and p1152 (rich)

I’ve replaced the EGR valve and DPFE, replaced the pcv valve, cleaned throttle body and intake plenum.

Mods
SCT X4 91 canned tune
Edlebrock victor jr intake manifold
BBK 78mm TB
Fender CAI
LTH
Hi,
What year, exactly is this, and did this issue start with any recent changes made? Much easier to help with specifics.More cold engine occurrence than hot?
Your canned tune isn’t helping anything, should get a custom tune-but as for the intermittent problem.
Have any more codes(or have you checked for ones in the absence of a CEL) since you replaced your EGR? Can you run a data log with your OBD-2 Scantool? If so- Drive it & catch the data for a more accurate response as to what’s occurring.
Run it through the PID’s and look for an O2 sensor that’s pegging & not correcting, as well as your fuel trim. Note the changes that occur when this happens.
Check all your grounds, Battery to block, block to Chassis, Battery to EEC.
1) Have you checked your TPS, it’s output voltage?
2) You’d mentioned cleaning things up, did you clean your MAF with CRC MAF cleaner?
3) It May very well be a plug wire arc, or a fouled plug, Fire the car off in the dark & look for stray arc’s. Check your cap for a crack, rotor, wire routing near headers, etc, & your electrical connections.
4) Check your IACV for proper function & no air leaks. Do a once over on all vacuum lines, replace any questionable’s.
5) Coolant level check & verify function of your Engine CTS.
Good luck!
-John

I can offer you info I found in my "CHILTON FORD MUSTANG 1994-04 Repair Manual 26608." BTW, you can get your own from Amazon or borrow from public library. Go to section 0-23 and on the bottom right under number 8. - Engine "lopes" while idling or idles erratically
1. Vacuum leaks - Check mounting bolts at the intake manifold for tightness. Make sure all vacuum hoses are connected and in good condition. Use a stethoscope or length of fuel hose held against your ear to listen for leaks while engine is running. A hissing sound will be heard. Also use soapy water to find leaks. Check the intake manifold gasket surfaces. (from me - make sure no cracks in the intake manifold).
2. Leaking EGR valve or plugged PCV valve.
3. Air filter clogged.
4. Fuel pump not delivering sufficient fuel.
5. Leaking head gasket. Perform cylinder compression check.
6. Timing chain(s) worn.
7. Camshaft lobes worn.
8. Valves burned or otherwise leaking.
9. Ignition timing out of alignment.
10. Ignition system not operating properly.
11. Fuel Injection or engine control systems malfunctioning.

Each of the above has a reference to elsewhere in the manual where you get the detail info.
Good luck!
 

08GT500

Active Member
Jul 12, 2018
898
139
53
50
Massachusetts
Hi,

My car is having a very strange idling issue.

When you first start it up for the first maybe 10 seconds it idles consistently. After that it’s like it’s got a Bluetooth cam you can turn on and off that lopes to the moon. In essence, it surges from 400-1000 RPMS periodically. Every now and then it’ll balance out and idle consistently, then boom, it’s cammed again.

Whenever I’m cruising with light throttle input it’ll surge and buck no matter the gear/rpms. Occasionally it will become so bad that it’s almost like it’s building up pressure when initially lifting off the pedal. Push down on the pedal and it feels like it keeps building pressure till it finally sputters, clears its throat, and lurches.

What confuses me the most, is the car performs fine under full throttle in the rpms, if not flawlessly. If you’re cruising but slowing applying throttle it’ll feel somewhat sluggish and then once the pedal is matted it feels like it clears its throat and goes.

I’m pretty stuck!! Any help is GREATLY appreciated!

codes I’ve gotten: p0401 (EGR insufficient flow) and p1152 (rich)

I’ve replaced the EGR valve and DPFE, replaced the pcv valve, cleaned throttle body and intake plenum.

Mods
SCT X4 91 canned tune
Edlebrock victor jr intake manifold
BBK 78mm TB
Fender CAI
LTH
Hi,
There’s useful diagnostics data here that may be quite helpful along with with my previously post.

Additionally,
1) What injector size are you running and are they calibrated to the MAF being run, are you running an oval or conical CAI filter, as many MAF’s (Such as PRO-M) are designed to run a specific design and will create idle issues running other than which type calibrated for.
What ID is your MAF(mm or In. (25.4mm=1”))
2) Running a fuel pressure gauge on the rail? Install temporary F.P. Gauge to Schraeder valve.& verify no leaks using initial pump prime prior to starting engine. Measurement with regulator connected, disconnected?
Pull the F.Pressure regulator line, leave connected to regulator, cautiously pull a slight vacuum orally, strong fuel taste/presence indicates regulator diaphragm rupture, Replace.
3) Pull your MAF wiring as the engine is running, it should sputter & run awful or stall entirely. If not, there’s an issue with your MAF/associated wiring.
-Has any routine maintenance been performed on the vehicle,preceding its current idle issues?
-The DPFE usually melts or water intrustion causes it to fail. Did your efforts clear the codes?
- Have you hooked up a vacuum gauge to the motor? What are you pulling at idle?
—>When monitoring the engine’s PID’s with engine running(Live streaming data, or Freezeframe, drive cycle, etc), be certain to record and printout when the anomaly has occurred, view all data, 02’s, IACV, Fuel pressure, Timing, fuel trim, TPS, and compare as recorded- frame by frame.
- OBD-2 ScanTools that perform advanced diagnostics should be as common as a Testlight in the modern toolbox. They’re inexpensive, easy to learn how to use to their potential, cannot “hurt” a vehicle, (read Only Data).
They can/will save you thousands of dollars, they can be run on 99% of OBD-2 vehicles, absolutely vital to use the vehicles own CPU data for diagnostics). if you’d like a recommendation on an inexpensive yet excellent unit to buy, user friendly, annually updateable free of charge, please ask. Happy to help.
QUESTIONS REGARDING THE INTAKE SETUP, SMALL CHANGES WILLGREATLY IMPROVE LOW END RESPONSE..
—Can you clarify other bolt on’s used, if previous owner installed mod’s, & uncertain of other supporting mod’s, E.G.,Cams Or heads/porting, etc, information will be useful, Posting an engine picture is helpful.
- If you’re running OE heads, to a Victor, Jr EFI, to a 78mm T.Body, if CAI piping then alter’s size excessively less than circular Mil’s equivalent to intake flow, or MAF to T.Body size reduces excessively, turbulent airflow will cause low end power loss, poor MAF vacuum system metering, idle issues.
-Has the motor run at a normal idle without fluctuation previously with the build and canned SCT tune currently being run, has low end power always been a bit “lacking”?.
-When the motor runs well at WOT, it runs on a completely different set of programming values versus driving the vehicle under normal circumstances.
Look forward to the additional information to narrow the issue down & assist in its repair.
If you’ve already satisfied this, please post that, so the thread is listed as concluded.
Regards,
-John
 
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