Hello everyone,

So I have a question.

This throttle body was on the car when I purchased it, since I purchased it, I have been battling MAF codes.

Recently I installed a stock TB, and went for a long drive. Codes never showed, one of the smoothest rides of its life.

Long story short, that TB didn't work out, sticky throttle, and a slight mishap which resulted in the unit being unusable at this time.

I threw the 58MM TB back on, and after about 10-15mins, I got the code.

So I am kind of stuck. Is there any way to restrict airflow to remain in the MAF parameters?

Is there a service out there that sells rebuilt stock units?

 

I was always somewhat dubious about the larger throttle bodies. The GMPP big block crate engine (502HP) used the 48mm TB to make over 500HP. That doesn't mean it was ideal, but it supported 500+HP.

There are used TPI throttle bodies for sale in various places, but they are likely to be as worn as what you installed previously. However, if the original throttle body is worn, it can be repaired.

https://www.ebay.com/itm/124336971784

https://www.throttleshaftrepair.com/


A larger question may about the condition of the MAF sensor. Is it stock? Does it still have the required screens? Is it installed in the stock location? Does it have the original inlet ducts and filter, or a hot-air intake cone?

 

The MAF sensor is relatively new. It's a Delphi from HERE. Bought last Summer.

The rest of the system is as stock as it can be, I've got the standard snorkel, and filters. I might not have tested the other TB long enough to get it to display the code, but it was a pretty hot day and I went down some pretty rough roads, and the code never triggered, was a dream except for that sticky throttle. 58MM back on, and a code within 15mins of driving is certainly suspect.

My problem currently with the stock unit is the head of the little screw that holds the spring to the throttle lever broke off when I was tightening it, cause my dumbzz thought taking the screw out, then tightening the spring more would help. Lemme tell you, much frustration, and no help. Turns out it was sticking on the TPS side, and now I've got a little mess on my hands. The spring popped apart, so instead of a sticky throttle, and small fry issues, im back to a code 33 and a slightly disassembled stock piece.

 

I found an alleged NOS Throttle Body on Ebay, hopefully this is a true NOS unit. Coming from Canada so it will take some time.

We shall see!

 

Seemed like I remembered there were some differences in the IAC on the earlier and later throttle bodies. I know there some plenum differences and did a quick search to find this from an old post.
Maybe that's an later model throttle body and if the 88 IAC from the stock 88 T/B was used it would be giving you some kind of vacuum leak? I do not know for sure if this could be the problem or not. However, if I were you I would do some research around that before spending any money on a new throttle body if just using a later model IAC would "fix it".

 

The difference can be seen on the back of the throttle body. 89-92 iac passage connects between the bores of Throttlebody blades. 85-88 uses a triangle hole to get vacuum from plenum.

 

Well both throttle bodies had an IAC preinstalled. Both seemed to work as intended, but it's hard to say, I didn't try swapping them. Again, it's only after driving for a period of time with the bigger TB. I have to assume its pulling in too much air and throwing the MAF just outside of parameters.

 

Have you tried to run with the TPS adjusted toward the higher end of the allowable range? After setting minumin air, the TPS could be set to closer to 0.60V at closed throttle to see if that makes the ECM math happier.

 

Not to hijack this thread but Vader do you think there could be any performance gain by running TPS voltage a little higher like .60V? I heard mention on a few old threads about that but nothing conclusive. I was curious if it would give a modded TPI better throttle response.

 

I will have to try that tomorrow, interesting idea!

 

I will try too, nothing to lose in giving it a shot. I saw some guys on the vette forum claimed better throttle response.

 

Well shoot, my tps doesn't go lower than 0.61 and I was under the impression that was a little too high, but the engine does seem to run pretty good so I guess I'll have to wait and see your results.

 

I set mine to 0.61 and the car ran good but didn't notice much if anything in better throttle response, maybe a little more crisp when cold but hard telling for sure.

 

Update!

As of 8/30/21 I installed a NOS 48mm Throttle Body, she runs, idles, and drives like a dream now. This is the first time in the almost 7 years of owning this car, that I am driving it with (almost) no problems.

No more codes for anything, and I've done extensive testing. My car is finally happy.

 

Apparently, the aftermarket missed a few details and skipped some of the study in their homework.

 

I find it strange that there are no aftermarket 48mm TBs. It is what it is, I suppose. Im throughly enjoying driving without any engine or computer complications.

Now its just a manner of taking care of the minor annoyances, some squeaks and chirps, bad paint, misaligned hatch/body panels.

I do love this car and it took me almost 7 years to get it reasonably drivable.

Hopefully I can give her a bright future.