Did you check out your injectors?
If they turned out to be ok as well as the prev. one, you might want to check into the O2 sensor and/or CTS.

Pull the plug on the CTS, measure resistance and come back.
Check this when it has been shut off overnight.
Also, note the ambient temperature when you check this.
IIRC, if it´s 75-80 degrees F outside, and the car has sat overnight, it should read something like 4000-4500 ohms, could be wrong here, but I can check it later in the FSM.

If you have a scanner, you could do the same thing, just compare outside and operating temps, and see if the O2 sensor readings change fast.

 

LOL! Thanks for the reply. I'll figure it out eventually.

I'm tempted to put a carb on it.

 

I replaced my injectors last yr but I'll check them again. I also replaced the CTS and O2 sensors along with the fuel pump and filter. I've tested the TPS and even swapped one from another intake. I also tried a different MAP sensor. Could it be possible that the MAP sensor is dirty? Is there a way to clean it?

 

I´m not a big fan of cleaning stuff anymore, I soaked the IAC in WD40 and let it sit overnight.
Day after I put it in again, only to observe it didn´t help anything.
Then I decided to leave the old IAC in the TB, disconnect it, plug in a new IAC just to see if the ECM was commanding it when I started the engine and flipped the throttle a little bit.
The shaft in the new IAC moved in and out just very slightly, so I thought, OK so the ECM is talking to it in some way.
Put the new IAC in, did the reset... fixed.
That much for cleaning and going through disconnecting the TB one time too much.
If you have a voltmeter, put it on ohms, disconnect the IAC connector, put the leads on the upper two terminals (If the securing lip of the connector points uppwards, then you have the upper two terminals being A and B, the lower are C and D).
You should read something like 40-80 ohms, the lower two, C and D should read the same.
My old one read 62 ohms on both upper and lower terminals, the new one is arround 58.
If you get very out of range readings, it´s really shot.
I know it doesn´t help much, but it´s a free test.
Map sensor, I don´t know, they rarely break.
I don´t know about the internals of a MAP sensor, it´s a solenoid if I´m not mistaking and therefore delicate.
Otherwise I would have put pressure air on it to clean it................. I didn´t say this, keep that in mind.............
A scanner would show a MAP reading lets say, arround 1.35 volts when idling IIRC.
So you could try to hook up a voltmeter to two of three MAP wires, in the same way you test a TPS sensor, but now with engine running.
The blk/pnk wire on the connector is sensor ground, the lt grn wire is MAP signal and the gry wire is the 5 volt ref.
You have three wires on the TPS as well, and there you are NOT dealing with the gry wire wich is 5 volt ref, so if my logic works here, you should be dealing with the black/pink and the light green wire on the MAP sensor connector.
Another test from the FSM says you can check the sensor ground circuit by probing the sensor connector ground wire (blk/pnk) to battery power with a test light, does it light (even with ign off) than that path is OK.
And if you turn on ign. and connect a voltmeter between the blk/pnk and gry wire, you should be getting 5 volts.
It also says in the FSM, that in case of a MAP failure, the ECM will substitute a fixed MAP value and use the TPS to control fuel delivery.
The ECM receives information as a signal voltage that will vary from 1-1.5 volts at idle to 4-4.8 volts at WOT.
Almost the same value as for the TPS.

See what you can do with this.

 

This is an old thread but was helpful, I just installed my ZZ4 short block into my stock 89 auto coup and it was having a cold start problem, hesitation and backfire until warmed up.

Turns out it runs perfectly without the MAF sensor hooked up - I'm biking tomorrow to pick it up a new one - so thrilled considering it could have been anything since I've seen so many threads of a cold start hesitation problem without resolution. I even saw some that sold their vette's because of this.

Nice to know the '89 runs without the MAF sensor hooked up (though it sends a code) - and uses a default setting. I wouldn't want to ride it that way since it'll probably do a little damage.

The 25 year old MAF sure looks like its delicate - I probably kicked it a little after taking it off numerous times.

 

It never flashed a code till I disconnected the MAF when it ran great.

I'm replacing the 2 MAF relays and the fuel pump relay while I'm at it.

 

There are so many threads that have hesitation only cold start problems that never get resolved. Many having problems in the ECM open loop mode where it doesn't use the O2 sensor while cold, there should be a simple list (year dependent, '89 would be):

TPS = 0.54 V
No vacuum leaks
Fuel pressure good/ Injectors no leaking
Fuel Filter Clean
ECM good
ECM coolant sensor in front good
Codes Set
Relays OK
Yadda Yadda Yadda

and checking that when the MAF is disconnected that it doesn't make a difference, should be checked off at the start of this fix.

 

I finally took mine to a mechanic/tuner that knew what he was doing. He found serveral minor things but the major thing causing the hesitation was bad fuel injectors. The multec injectors were only 2-3 years old but he said the crappy fuel really hurts them if the car sits a lot. So I replaced the injectors with Bosh IIIs from Fuel Injector Connection and it runs great now! I can hardly believe it. No hesitation at all! I'm getting a final tune done on it today so it may run even better after that.

If anyone is in the PA/MD area and needs a great mechanic/tuner. Southern Stables Automotive is the place to go.
http://southernstablesautomotive.com/

 

That's great news - I would definitely add fuel injectors to that list of hesitation causes.

So many things could cause a cold hesitation problem, I just installed my new MAF sensor and relays and I am thrilled too. I just wanted to add that I did try cleaning my MAF sensor and that did not help, the sensor looked fine and the platinum wire looked shiny.

I think I've just had the best ride in my vette ever today - I just put a bottle of bubbly in the fridge to celebrate this weekend of my successful completion of my ZZ4 short block in my stock engine.

There were times I had a little voice saying I'm over my head on this project, I just ignored those voices. There should be an elite club for people that have installed a new engine in a vette. I know people do this for a living, but it is something else for non mechanic to achieve this in their garage.

The shiny valve covers are just placeholders, I've got the stock valve covers off and will enjoying cleaning them up. The funny thing with installing a new shortblock is that you can't see it at all.