Keep OEM PCM and tune it or go Aftermarket PCM?

I have driven my 5.3 LM4 conversion in a 1988 944 for about 3000 miles since last year and now the goal is to make everything "right". I have a list of things I need to do to make the car 100% finished and one of the most important items is to get it to run correctly. It runs OK but it has several annoying driveability issues that need to be fixed by tuning the PCM. It bucks at low speeds, you have to put your foot on the gas when you start it and eventually the IAC will take over, the tach reads double, etc. I have a friend who has HP Tuners that I can borrow and I planned on using HP Tuners for the medium to store and send the information from my PCM to a tuner. I understand how HP Tuners works (it's very complicated) and it would take me months to figure it out so I don't want to attempt to tune my PCM for my self. We have no one in our area that I could take my car to that I would trust to make my car right.

My question to you is should I spend the $400 for credits and tuning on my stock PCM or should I purchase one of the aftermarket PCMs such as the Holley unit for about $1000?

The engine combination I have is:
5.3 LM4 long block from a 2003 Trail blazer
All external components (intake, front end accessories) from a 1999 Firebird LS1
PCM is from a 1999 Firebird LS1
Sensors and ignition coils from the 2003 Trail Blazer
Painless LS wiring harness
Brian Tooley Stage II truck cam (In. dur. @.050 212, Ex. dur. @.050 218, .553 lift, 111 LSA)
Brian Tooley valve springs
Renegade Hybrids shorty headers
K&N cone type air filter with MAF sensor in the intake tube about 15" from the throttle body

If the recommendation is to tune the stock PCM, does anyone have a recommendation for a tuner? Thanks, Gil

seeing as the car is already up and running on a stock pcm id keep working with it. if you didnt already have a swap harness and a pcm id lean towards aftermarket, but a stock pcm is more than capable. it only takes 2 hp tuner credits to unlock your pcm, thats $100 to unlock it, not $400.

hptuners isnt that difficult to work with, its just very intimidating because there are so many tables. the reality is there is a small amount of them you need to work with to sort your issues out. really what you would need to do is start by sorting out the idle airflow (likely need to adjust the throttle blade a little) and it will likely start and idle a lot better. from there you need to fail the maf and tune the ve table, then reenable the maf and tune the airflow table. really its just driving around while logging, and copy and pasting/multiplying the histogram data. since you have access to the cable already, and are already buying credits, i say do a little reading on the tuning process for that model pcm and give it a go. the key is every time you make adjustments save your tune as a new file, that way if you mess up you just go back a step. and in the end if it doesnt work out, flash the original tune back in and then call a tuner.

Like Sharkey says, your car is already up and running. You have a very mild build and the stock pcm will work extremely well. I know people making 1000+ hp on a stock pcm. There are several mail order tuners that do good work. I can send you the email for one if needed that I use.

I will go with the HP Tuners route but I don’t have the “stock tune” for my PCM. My PCM had been reflashed before I bought it and I sent it to a mail order tuner to get reflashed again last year. The second reflash helped with some problems and created some new ones. It seems as though the going rate for an email tune is $300. Sharkey, I might attempt to do the tuning by myself if I had the stock tune to go back to but I think it would be quicker to pay someone that knows what they are doing. I would appreciate any suggestions where I can the tuning done. I have talked to tuners in Texas ( mail order tuner.com) and in North Carolina (pcmofnc.com) that seem competent but I am open to suggestions for someone else. I really appreciate your help, Gil

Tunning my conversion was a breeze with HP Tuners. Decided to make the investment and learn myself. Just watched a bunch of youtube videos. Goatrope Garage has a great tunning series. Mail order tunes will get you in the ballpark and the car running but to get your fueling spot on, it will take logging as every car is different. And in the future if you make any mods, you once again have to modify the tune. This will get very expensive. A simple CAI reconfiguration will require an airflow/fueling table tweak on these motors.

You do not really need your stock tune. Sounds like your car is at least running. You can just use your current tune, and work off of that. If it is really jacked, sometimes its best to start over. You can tell what tune they flashed by connecting to hptuners. They prob started with a stock manual camaro or vette tune. My PCM came with a stock 07 C06 Vette tune.

I'm proving my ignorance here-what is a CAI reconfiguration? Also, my friend's version of HP Tuners is not the latest version. It is at least 2-3 years old. Will this be a problem?

Cold Air Intake. I reconfigured my piping from the throttle body and fueling was off. Had to tweak my maf and VE tables.

No should not be a problem. His version should work fine or he can just download the latest update.