Rough Idle-'89 454 Tbi

I just installed a 454 TBI long block in my '89 Silverado. When I first fired it up it ran great. I adjusted the IAC (which I shouldn't have) to get the engine up to 1500 rpm's for about 15 minutes. I backed the IAC off after 15 mins (back to around 1000 rpm's) and it ran pretty rough (didn't want to stay running). I drove it and it was real hesitant, stalled a few times when I stopped, but when I gave it about half throttle it would take off and run great, especially under a load or going up a hill. I took it to a shop and they said one of the injectors was barely dropping any fuel, so I had the injectors rebuilt. I also replaced the fuel filter, EGR valve, O2 sensor, and now the truck idles worse. When it is cold, it has an irratic fast idle (it speeds up and slows down). When it comes down off irratic fast idle, it really runs rough. Now I am getting an occasional SES light. I checked the codes and I am getting a 44 code (lean exhaust). I disconnected the battery for a minute, but still getting an occasional SES light with the 44 code. I took it back to the same shop that said one of the injectors was bad, and they say one injector still has an abnormal spray pattern. I called the injector place and they said they have rarely seen the TBI injectors go bad, especially after having them rebuilt. The mechanic said he checked everything (fuel pressure, vacuum leaks, injector voltage, etc) and he is stumped too! Any suggestions would be highly appreciated! Thanks, Tim

do you think the IAC valve is good? Have you run the trouble code troubleshooting diag. chart for that code? I bought two new injectors for my 92 350 ...I think they were about $200 Each...GM really gets you on those.
I don't think the injectors just went bad. Did the injectors work fine before the engine swap? What did you adjust? I believe there is certain way you set the IAC valve and that it.... if its not set properly then its never going to run right. You have a GM shop manual?

Don't know if the IAC valve is good. I don't have a manual to see how to check it, or adjust it. The shop I had it at supposidly checked all the sensors and everything they could think of and couldn't find anything wrong, other than one injector having an abnormal spray pattern. The truck seemed to idle fine before the engine swap. It was knocking so loud, so I didn't drive it. The only thing I adjusted was the throttle positioning sensor (to keep the new engine running at about 1500 rpm's for about 15 minutes). I later found out that the tps is factory set and you should never touch it. I adjusted it back down, but it probably isn't exactly where it should be. It hasn't idled right since the engine swap. The truck did sit for atleast a year (before the engine swap), so I changed the fuel filter and put new gas and gas treatment, along with injector cleaner in it , but no luck. Maybe the fuel system needs to be flushed? I called another shop and they said to replace the fuel pump relay. Would that cause a rough idle and a 44 code (lean exhaust)? Thanks

Adjusting the TPS is not very hard if you know a few specifications. The problem is most people do not have a factory service manual handy and Haynes and Chilton manuals are not in depth enough with their small amount of information. You should have a 5 volt referenve signal to the sensor and you adjust the TPS according to the output voltage to the computer, I am not sure where it is supposed to be set but if you get a service manual you should be able to find it. As far as one fuel injector barely spraying fuel, it could be a bad injector. If your mechanic had an oscilliscope he could put the scope on it and see how long the injectors were opening for. that could tell him if there was a problem in that circuit. Or since both are right next to each other you could look at the spray yourself with a timing light and swap the two electrical connectors and see if the injector that barely sprays moves with the connector or stays with the injector.

ok in your original post you said you adjusted the IAC. I know if the IAC is screwed with and set wrong or its faulity truck won't idle for crap.
I have a 92 K 1500 with a 350, I also have a GM Shop manual. I'll look up code 44. Are you getting any other codes? I know if one of your injectors is screwed...your truck will run like crap too, but why would the injector fail just when you did the engine swap. TPS are adjustable and I think its .5 volts on that truck. Are you sure you don't have any vaccum leaks and that the timing is set correctly? I don't think the realy would affect that but swap it out and see, I don't they they are that expensive. I'll post more on the code 44 tomorrow.

I had another shop look at it and they also said it appears one injector spray pattern is abnormal (after I just had them rebuilt). The place that rebuilt them put the injectors in wrong (Doctor Injector). The pins were parallel with the truck, but they should have been perpendicular. I thought it looked wrong when I picked the throttle body up, but the kid working there said the injectors will only go in one way. It turned out the injectors were reinstalled wrong. I took it back and he re-installed the injectors in the right position, but now I'm wondering what kind of job he did on rebuilding them! I'm going to take the tbi back to "Doctor Injector" and have the injectors re-checked before I invest anymore money.

ok then...maybe its the injectors. Yea you have to question someone who is in that business and they can't put the items back together correctly. I do remember thinking $$$ when I had an injector go bad. Since the truck had high milage and one bad injector I just replaced both of them since I plan to keep this truck for a while. That may be your entire problem. Normally the TBI units work good (since there's not much you can change) Don't bother with one of the holley units....I tried one of those and I never could get it right on a 92 TBI 350 engine. Holley support was non-helpful. About all you do on a TBI unit is to set or make sure the TPS voltage is right and thats it. Unless the IAC fails.