TBI issues-surging idle

[Greenlee]

I'm just getting this truck back together after a long rebuild. It's an 87' with a rebuilt crate 350. The computer and wire harness are from an 89' Suburban that ran great when I stripped it for parts for this truck. I have headers, a new 3 wire O2 sensor and dual exhaust. All fuel lines, gas tank, fuel pump etc. are new.

Issue: it runs great at start up. Sometimes it continues running great. Other times when it goes into closed loop it starts surging at idle. Sometimes it surges bad enough that it dies. It sometimes dies at stop signs. Other times it runs runs fine.

Over the weekend I got a check engine light shortly after I started it. This doesn't normally happen. I checked the code and got code 54. I have read up on this and code 54 is related to the fuel pump relay. It usually coincides with truck turning over and not starting. I haven't had a problem with it not starting.

Today I drove the truck to work and back a total of about 70 miles. This is the farthest I have ever driven the truck since putting it back together. This time I got a check engine light after driving on the freeway for about 20 minutes. The code this time is 32--EGR. I have been reading up on code 32 and most people don't have the symptoms I have. Some say code 32 can be caused by not having enough back pressure with headers and dual exhaust.

So to make a long story short, I have these random codes that may or may not have anything to do with the truck not wanting to idle after it warms up. Anyone have any ideas where I should start looking first? Thanks in advance for your help!
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[chris989]

My friend, I was just going to make a post about idle today too.

It is possible when entering closed loop the computer is reading vacuum vs rpm and trying to maintain a certain RPM. Are you using a scan tool or can you hook to your computer?

sidenote
I have replaced everything possible with my 89 TBI truck and I too randomly get idle issues still. I data log with tunerpro and nothing standing out as wrong. Just today, in a parking lot my idle goes to 950-1000 while sitting still. It has been months since this happened, come home, hook up the computer, nothing wrong and now the truck is good again.

I can only guess somewhere two values argue in code, for me i think it is something to due with AC vs a rise in engine temp. I think GM over complicated this TBI setup before they had a total grasp on it. There are so many variable that affect the idle i am not sure if mine can be found. I am very close to taking the TBI off and installing a carb with a manual choke.

chris

[chris989]

Greelee,

Any luck? I am sitting in my burb logging data as I type. Mine is not the IAC steps as I thought.
I think I have traced mine back to the hose to the MAP sensor/controller. the hose is hard plastic with ends pressed on. One of my ends was not secured great. That small vacuum variable was throwing my idle +/- 75 rpm.

The issue of closed loop is an issue. Until then it is not reading but running in a logic mode. IS it possible you are coming in and out of closed loop?

I am no expert, I hope I can help. If you are not data logging, TUnerpro is free, you only need to buy or make a cable.

Chris

[homemade87]

This may or may not help. I did the same as you. Did a rebuilt engine. got it all together and started and run fair with the surge you are talking about. Went threw all the stuff you guys are doing and with no help. I got frustated and decided to play with the timing. I had set the timing to 0 originally. I left the timing light in the tool box and started to change the timing by sound. After playing with it a few minutes the surge was gone and run great with better power. I had run it that way for about 15 years. I dont remember but I think is was advaced about 12*.It just did not like that 0* setting. Best I could figure is that the cam may have chaged things. It may be worth a few minutes of your time to look at this to see is it may help. If I remember correct I think mine started surging when it went into closed loop as well. Good luck.

[dustnx]

I have an 89 firebird I swapped a 92 chevy 1500 350 tbi into, had all kinds of problems with surging. Bought new chip, replaced a bunch of sensors, messed with timing, etc... still surged so bad it would die. Put new fuel filter on, changed plugs, distributor, all kinds of stuff. Come to find out, one of the rubber hoses inside the fuel tank that goes to the pump had a small crack in it and was sucking air when tank was below 1/2. Fixed the hose and its ran like a champ since then. Might not be the same problem with yours, as these TBI's seem to be a hassle in troubleshooting, shows a bad sensor here, etc etc etc... and never figure the problem out lol... But might be worth checking if you haven't already!

Good luck, I know how much of a hassle they are lol.

[Greenlee]

Thanks for the replies. I'm actually a fan of the TBI. I had an 88' GMC that I put over 200,000 miles on and had no trouble with it whatsoever.

I think most of my problems stem from the fact that I am attempting to do all this stuff myself and don't really know what the hell I'm doing.

Since I first posted this I learned that I had the wrong computer in the truck. I had bought a towing performance chip from Brian at Harris Performance (http://tbichips.com/). When I tried to use it the truck went into some sort of limp mode where the Check Engine light was quickly flashing and the truck would barely run at all. I sent the chip back to Harris Performance. He asked me for the four letter code on the stock chip, which was AKWA. From that he emailed me back that I was using computer 1228747 which was from a 1990 3/4 ton Suburban with a TH400 transmission. He said this would not lock the torque converter on my 700R4 and was also the reason his chip didn't work.

Turns out he was correct. I had used 1989 and 1990 Suburban's for parts. I thought I used the computer from the 89', but must have got it mixed up with the 90' computer. Brian re-programmed the chip not to read EGR and sent it back to me. (By the way, he did all this at no charge and is great to do business with if anyone is looking for a performance chip or to have one reprogrammed!)

When I got the chip back and put it in the correct 1227747 computer, I had some other weird symptoms at first. The truck would idle ok, but would fall on it's face when I gave it throttle. I checked my vacuum lines and it turned out the EGR wasn't even hooked up. Not sure if this matters since he programmed it not to look for EGR. I hooked up the EGR and have been driving the truck around. Now it seems to run almost perfect. I still feel like it surges a little at idle when I am at a stop light, but it's not bad enough to make the engine die. I'm not getting any more Check Engine lights or trouble codes so far.

I wish I knew how to do the data logging. For now I will just keep tinkering with it and driving it. It seems to be running better the more I drive.

[chris989]

It is very easy to data log

you only need a cable and the laptop. You want the cable with the four pins on the USB connecter, it makes it easy to ground out the pins to read codes.

Win ALDL is free.

http://www.aldlcable.com/sc/details.asp?item=aldlobd1u

http://www.aldlcable.com/sc/details.asp?item=aldlobd1u

You can also go to. they have everything you need to burn chips and see your performance in real time.

http://www.moates.net/