idle quality hard start when hot surge, etc

[junkyardwarrior]

Background:
'93 LX originally a 4 cylinder car. Pulled 2.3, installed 5.0. Installed A9L ECM. Also used a '93 GT automatic engine harness, MAF harness, used NEW O2 harness for 5 speed, '93 GT A/C harness and kept the original '93 2.3 trans harness (which does not have a NGS). Engine details: 5.0 Mahle flat tops, lightened crank, AFR165 heads, custom ED Curtis cam (218-232 @ .050 112 LSA, .550-ish lift), RPM II upper and lower intake, 70mm Professional products TB and EGR plate, 80mm PMAS MAF for 24 lb, 24lb injectors. Engine is FRESH. 1 3/4" BBK coated LT headers, catted H and a cheapie cat back.

Ok here is the deal. I've fooled with this thing for several days trying to figure out a decent idle. The ONLY way I've gotten any kind of idle is to flip the IAC over, put a spacer plate in between the IAC and TB, and in between the two holes that are in the spacer I milled a space out. After installing, I had to back the stop screw down (IAC disconnected). Reset TPS then disconnected battery and let it sit overnight. Started up next morning and it started right up, although a little rough. Drove it back and forth to work 2 days without touching anything. Had some time today and tried to fine tune the idle. Checked timing...10 deg spout out. Checked for vacuum leaks-none found (pressurized intake and used soap/water mix). The IAC being flipped was hitting the EGR coolant hose. So I bought a new IAC and installed it no spacers, and installed it the correct direction. Turned key, engine fired...went up to about 1500, then died. Restarted. Same thing. Restarted. Same thing. Restarted again. Throttled it with my foot and let the engine settle in...got to operating temp. Then removed throttle input and engine settled down to about 800, then started to "catch" itself...went up to about 1500, then died. Got out, unplugged IAC and set base idle to 1000 RPM (engine hot), shut engine off, then reset the TPS (got too high setting a code). Disconnected battery for about an hour. Back out, plugged the IAC back in, reinstalled battery cable and then restarted the engine. Surge like I never touched it.

What gets me is that even though base idle was set to 1000 RPM, during the surging, it would still drop to 800-900 RPM, then the IAC would open and it'd shoot back up to 1600-1700, then do it over and over again until I throttle it manually with my foot--then it'll stay at 1100. Push clutch in, it drops to 1000 and stays right there. How would RPM drop below 900 during a surge if the base idle is 1000?? Does the timing change or? I checked it with the light and it's rock steady. Spout out 10 deg. Spout in about 20 and it changes with TPS changes and throttle change.

At this point contemplating (1) selling the entire project, (2) possibly converting to carb (3) giving up altogether. Can't even drive it when it wants to die at every stop light or has to idle at 1500 RPM to stay running! Seems to have lots of power and it's fun to drive but the idle quality and lack of idle is taking ALL of the fun out of it.

Any help would be appreciated. Frustrated. Have been through the surging idle checklist and nothing is helping.

 

[jrichker]

In case you haven't seem this little gem, here are some clues to help solve your problem....

See the "Surging Idle Checklist for help with all your idle/stall problems.

The quick and easy way to dump the codes is in there too, and all you need to do it is a paper clip! The first two posts contain all the updates to the fixes. At last count there were 24 possible causes and fixes for surging idle/stall problems. I continue to update it as more people post fixes or ask questions.

 

[junkyardwarrior]

codes are:
44, 94 and 34. 34 I know is EGR and the TAD and TAB solenoids are installed, but nothing else is installed (no air pump, hoses, lines, etc). EGR is blocked off with a plate sandwiched between the manifold and the EGR valve.

Still baffles me how on earth it can surge with the base idle set to 1000 RPM. If it's 1000 RPM base, how can engine RPM drop below that and start the surge process?

 

[VibrantRedGT]

We through a lot of mods at the 92GT, if we didn't have the twEECer it wouldn't even be running. I know exactly what your going through. Being able to visually see the TPS volts, MAF volts, Injector Pulse Width, O2 Temps, fuel pressure, timing, etc. was so essential. We were able to adjust everything correctly and now its idles like a champ. So worth the $400. I wasn't a believer until this project. I would have been adjusting and adjusting still and probably wouldn't have hit it.

 

[lancec2c30]

How much vacuum are you pulling at idle? Say around 900-1000 rpm.

 

[jrichker]

1.) Put the correct O2 sensor harness and correct transmission harness in the car.
Originally Posted by 302EFI
The wires for the 02's and low oil did not change throughout the years, they are all in the same place.
The main ones you need to worry about are (on the harness end (ECU) that plugs into the 02 plug) is:
\- 1. Lightblue / yellow
- 2. White / Purple
- 3. Purple / Yellow
The White/Purple & Purple/Yellow gets looped for a automatic ECU
The Purple/Yellow & Lightblue/Yellow for a manual ECU

See Oxygen sensor Harnesses - Manual/Auto differences and year differences - Ford Mustang Forums : Corral.net Mustang Forum for more O2 sensor wiring harness info

Basic premise to use with transmission swaps:
Only run a auto trans O2 harness with an A9P
Only run a 5 speed trans O2 harness with an A9L
90 model year harness only works with 90 model cars without inspection/rework.
The 4 cylinder O2 harness uses 4 wire O2 sensors. It probably won’t work correctly without modifying it.

2.) Check the signal ground for the computer.

Signal ground troubleshooting 91-93 5.0 Mustangs

The computer pin 46 signal ground is a critical component: it provides ground for the TPS, ECT, EGR position sensor and ACT. Signal ground is used in many circuits that have analog inputs to isolate the electrical noise. It is always separate from power ground, although both may have a common connection origination point. Signal ground usually has some conditioning that reduces the electrical noise to prevent false readings

The gray/red wire (pin 46) is signal ground for the computer. It provides a dedicated
ground for the EGR, Baro, ACT, ECT, & TPS sensors as well as the ground to put the
computer into self test mode. If this ground is bad, none of the sensors mentioned will work properly. That will severely affect the car's performance. You will have hard starting, low power and drivability problems. What sometimes happens is that the test connector gray/red wire gets jumpered to power which either burns up the wiring or burns the trace off the pc board inside the computer. That trace connects pins 46 to pins 40 & 60. Only an experienced electronics technician can open the computer up & repair the trace if it burns up and creates an open circuit.

See http://www.stangnet.com/mustang-forums/749974-computer-issue.html#post7490537 for Joel5.0’s fix to the computer internal signal ground.


If the ground for the TPS goes bad, the TPS output voltage increases and the idle speed goes up.

Troubleshooting signal ground problems:
Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter.
1.) With the power off, measure the resistance between the computer test ground
(Gray/red wire) on the self test connector and battery ground. You should see less than
2.0 ohms.

2.) MAP circuit: Check the resistance between the gray/red wire on the MAP/BARO sensor and then the gray/red wire on the EGR and the same wire on the TPS. It should be less than 1 ohms. Higher resistance than 1 ohms indicates a problem with the 10 pin connector or the splice inside the main harness where the wire from the 10 pin connectors joins the rest of the gray/red wire. Next check the resistance between the gray/red wire and the negative battery cable. It should be less than 2.0 ohms.

3.) Engine mounted sensor circuit: Check the resistance between the gray/red wire on the TPS and battery ground. It should be less than 2.0 ohms. Higher resistance than 2.0 ohms indicates a problem with the 10 pin connector or the splice inside the main harness where the wire from the 10 pin connectors joins the rest of the gray/red wire.

 

[junkyardwarrior]

went through everything. Removed EGR, cleaned it-got ride of code 34 and EGR is working as it should be. Pressurized intake to about 6-8 psi and fixed a vacuum leak at the TPS and one at the IAC. No more leaks-in fact if I turn the engine to #8 TDC compression stroke, I can pressurize the intake and it'll HOLD pressure for about 15 minutes. The only other leak is at the throttle body-where the shaft goes through the throttle body itself, and it's not much of a leak.

Removed battery cable (engine at 190°). Unplugged IAC. removed SPOUT. Reinstalled battery cable. Started engine and attempted to set base at 600 RPM. I can't get it down that low-it wants to surge and then it dies. I set base at 700 RPM which took some messing with the throttle to hold 700 RPM (kept wanting to surge but I could "feather" the throttle a little to get it to stay put). 700 is verified on a calibrated inductive tach. Shut engine off, checked TPS (.94). Removed battery cable. Ate lunch. Hour later, reconnected the IAC, spout, and connected battery. Started engine, surged immediately. Feathered throttle to get it to hold about 800 RPM...it stayed there for a minute then started the surging again. Called neighbor guy over to help me keep it running...he got it to stay put at 800 RPM and I checked MAF voltage-it was 1.01 @ 800 RPM. Just as soon as I disconnected the VOM, the surging started in again. Only codes left are 44 and 94...and the air injection system is inoperative. Solenoids are in place but air pump is gone and so are all of the tubes. All holes for air inj are blocked off (the heads and the tube on the H pipe).

Thing runs great WOT. At about 1200-1800 RPM holding a steady speed in any gear, it wants to "trailer hitch"....I can hear the trans clunking, the rear end, and driveshaft all making noises. Above that it kind of smooths out enough to be satisfying to drive. Power delivery from 1200 to 6200 is smooth; then we get into fuel/ign cut at about 6300-ish. That's fine with me...it's not very often it needs to be revved that high anyway. Haven't logged MAF voltage other than idle. Same with TPS and ECT.

One other note worth mentioning is that there is a high pitch whistle at idle speeds...sounds exactly like a vacuum leak but the whistle comes from the upper intake. I used a stethascope to locate it...it's directly behind the EGR plate somewhere (RPM II upper and lower intakes). Sounds like it's right in the middle of where the "vee" part of the upper intake joins the throttle body area. Like I said it sounds exactly like a vacuum leak but if it holds pressure how can it be??? Remvoed upper intake to inspect and the gaskets are all perfect. Fuel pressure 40 psi-pump brand new Walbro 255. Drops to around 30 with vacuum hose reconnected.

I'm finding this a challenge...I feel like someday I'll get it whooped but I need assistance in doing so. IF it were a 2.3 turbo (SVO or TC) I would've had it figured out by now. Had and messed with a few of those but this is my first injected V8....and of all of the 2.3's, none had idle surging issues. This engine is not stock. AFR165's, Ed Curtis camshaft, RPM II upper & lower, 70mm Professional products TB and EGR plate, 80mm PMAS MAF and matching cone filter, BBK LT headers.

 

[jrichker]

With an aftermarket cam, your surge and low speed problems may be caused by the cam grind. Check with the cam supplier and see that they say about idle characteristics.

Be sure the cone filter isn't pulling air from the engine compartment. The turbulence and heat will cause airflow problems through the MAF. The cone filter needs to draw air from the inner fenderwell. If the cone filter does draw air from the inner fenderwell, try clocking the MAF. That means you rotate the MAF housing in small increments to see if there is a position where the engine settles down and runs smoother.