Poor Idle Until Fuel Pressure Drops

[89gtsleeper]

I picked up an 88 5.0 w/ aod recently. When the car is completely cold, it starts every time but will idle at like 400-550 rpm's it's amazing the car doesn't die, but it keeps going. No throttle response at this point. After about 3-5 minutes of letting it sit like that, then it immediately bounces up to about 750-800 which is where it should be. Then the idle just stays right there. I went out and watched the fuel pressure gauge yesterday during all of this. Fuel pressure sits right at about 40 while the idle is low. Then it drops to about 33 when the idle finally jumps to where it should be. What would cause this and how can I correct it?

Car has aeromotive adjustable fpr. Timing set to 10 degrees. Car was swapped to mass air by PO, but they screwed it up. First, they put in an A9L instead of an A9P. Still has an aod trans and matching O2 harness. they did run the 4 wires from the meter to the correct pin locations, but they did not move the wires from 51 to 38 or 11 to 32. Could the mass air have anything to do with this?

 

[89gtsleeper]

I also already ordered a new IAC just cause the other looks ancient and dirty and it bothers me. Putting that on tomorrow.

Something else worth noting is that even once the idle really smoothed out and I'm ready to drive, if I put the car into any reverse or forward gear, the rpm's drop to about 600 and the car struggles to get moving until the rpm's get up to about 800-900. Under normal driving, the car generally is very weak and not very responsive until around 1800-2000 then it acts closer to a normal car with some throttle response. In the pre 1800 rpm area there is a lot of stumbling and popping caused by different right foot strategies.

 

[mikestang63]

run the codes

 

[jrichker]

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.

 

[89gtsleeper]

New IAC installed. Just replaced fuel pump and upgraded it to a walbro 255, which was definitely needed, but probably not related to my current problems. Did the KOEO AND KOER tests. The only thing I come up with is a code 95 on the KOEO. This is happening because the previous owner who did the mass air conversion did not run a wire from the FP relay to pin 19. One thing I have read about this is that some people report having stumbling and issues on deceleration related to this. That is something else the car really suffers from. I've noticed that at driving speeds then letting off to cruise to a stop light, the vacuum jumps to about 22-24" and the car starts having a bunch of tailpipe popping... Definitely not coming from the intake. However, if I put the car in neutral immediately when I let off the accelerator, the vacuum goes to a normal idle range of around 16-20" as I coast to a stop. Then the car seems to take off fine.

 

[jrichker]

Do not run an A9L with an automatic transmission and auto trans O2 sensor harness; it will damage the computer. The proper computer to run with an auto trans is the A9P. You need to fix that problem first.

After and only after you have gotten the alphabet soup Mass Air conversion straightened up, dump the codes and post them here.

Dump codes sticky

Look at the top of the 5.0 Tech forum where the sticky threads are posted. One of them is how to dump the computer codes. Codes may be present even if the CEL (Check Engine Light) isn’t on. You don’t need a code reader or scanner – all you need is a paper clip, or if your lady friend has a hair pin, that will do the job.
I highly suggest that you read it and follow the instructions to dump the codes. http://www.stangnet.com/mustang-forums/threads/how-to-pull-codes-from-eec4.889006/

 

[89gtsleeper]

I ordered the a9p replacement from cardone. Freakin back ordered for a month. May have to park this thing for awhile. Definitely think this has something to do with my problems. Also think I found out something else. The car has had a vortech blower added to it since it was running properly. The line from the passenger valve cover breather to the throttle body was still in place. Removed that and plugged both ends. Car ran really well for about a mile or two then started bucking and backfiring to the point I almost couldn't get it home. Replaced the distributor cap as the connections seemed a bit worn. Reset idle. Now tps won't go unde about 1.1v on key on. Car drives okay for a mile although it Idles high, then bogs and goes crazy again.

 

[jrichker]

Have you dumped the codes? the TPS problem tells me that there are other problems that you will not find unless you dump the codes.

 

[89gtsleeper]

Son of a B!!! I finally got fed up after trying nearly everything else. I pulled the custom chip off the car that the tuner put on it. Timing at 10 degrees. Fuel pressure at 40 with vacuum off and plugged. Started right up, but idle was super high. However, it was a really smooth idle. Did an idle reset, backed it way off to get idle under control. Drained the comp to reset idle.. Started right up. Idles super smooth. Car doesn't shake. No driveability issues. Strong smell of gas gone. No backfiring. No stuttering from low Rpm's. I realize I can't run any boost like this as detonation is going to occur, but it is running very well. Wondering if I should consider a new tuner or if I should just say eff it and get a btm/fmu and be done with it for now.

 

[89gtsleeper]

For the record I did dump the codes multiple times before this and could only come up with a single code because of the pin 19 wire not being run to the fuel pump relay under drivers seat during the mass air swap. Ran thigh almost everything on the surging idle checklist and everything kept looking good for the most part. That's why this whole thing has been so frustrating.

 

[mikestang63]

BAMA chip?

 

[jrichker]

Did you dump both key on engine off and key on engine running codes?

 

[89gtsleeper]

Did you dump both key on engine off and key on engine running codes?

I did. Only came up with the KOER code 95.

 

[89gtsleeper]

BAMA chip?

Chip is a blue chip with 4 tune switch. Looks just like the BAMA ones on American muscle website. Tuner used binary editor to create the new tune.

 

[a91what]

Try cleaning the j port connections with a very fine sandpaper or Emory cloth, wipe them clean with alcohol. Aply a very small skim of dielectric and reinstall the chip, a bad connection can cause headaches. If this does not work get a new chip flashed.