Stumble when letting of throttle @ idle

[87gninpa]

Just got this car a week or so ago and finally getting into it. Car actually ran well when I picked it up, but was in need of some basic maintenance. It was also showing a code for bad O2. Car is bone stock, even has stock chip. Here is what Ive done:

New O2
Plugs (.35 gap)
Wires
Air Filter
Fuel Filter
Replaced all vacuum lines
Cleaned TB & Iac
Reset ECM
Set Iac & TPS correctly

Car does have a decent header leak (BLM @ 145 at idle) which will be fixed soon.

Here is what the car is doing; it will start and idle nicely but when I give it any throttle it wants to die when it comes back to idle, then rev up quickyl and idle fine again. It doesnt hesitate at all when giving it throttle, just when it comes back to idle.

Did the MAF tap and unplugging it made it run worse actually so guessing thats ok.

Any ideas are appreciated.

 

[chops]

I reccomend taking care of the exaust leak first ! Blm should be 128 even 130 is fine at idle also. Get rid of those stock injectors get a set of 42pnds with chip and a bigger fuel pump and take it from there

 

[87gninpa]

I reccomend taking care of the exaust leak first ! Blm should be 128 even 130 is fine at idle also. Get rid of those stock injectors get a set of 42pnds with chip and a bigger fuel pump and take it from there

Yea, i know where the blms should be, but thats not causing my current issue.

There is no need to get bigger injectors, wont fix my problem. Have to get the car running correctly before you start throwing parts at it.

Anyone have any useful suggestions?

 

[scottyb]

My car never ran well with the stock chip.

 

[87gninpa]

My car never ran well with the stock chip.

Yea, Im not a huge fan either and fully plan on replacing the chip with a TT eventually. However, I would like to get the car running properly as is at the moment. It was running fine the other day before I replaced the above parts, so the chip is not the issue at the moment. Just need to get it running right for inspection on saturday then i can really dig into it.

 

[notacarlo]

Do you have a vac gauge? Seems like you still may have a charge air leak somewhere.

42# injectors.....so 1999. :biggrin:

If you do have a vac gauge, what's it reading at idle in gear?

 

[87gninpa]

Do you have a vac gauge? Seems like you still may have a charge air leak somewhere.

42# injectors.....so 1999. :biggrin:

If you do have a vac gauge, what's it reading at idle in gear?

I do, will hook it up when i get home tonight.

 

[gn4u2c]

It ran good the first day and then its all down hill LOL... sounds like every other story on this forum.... J/K:biggrin: Make sure you have the intercooler hoses back on correctly with no leaks, also check the core I have seen some leakers.

Think what else you have done that could have changed the way it runs... did you get gas somewhere.. did you fool with any thing and forget ie... vac line off or something weird like that. Was it running fine before you started swapping parts? did you crack a plug use cheepo wires... pull a terminal lose on the coil taking old wires off...

To me your 100% wasting you time adjusting anything until you fix the exhaust leak. I would do that then start fresh.

Best of luck these cars are so much fun WHEN they run right even stock.

 

[87gninpa]

Yea, I know the exhaust leak definitely needs to be fixed. Trying to find a nice set of stock headers as we speak.

Hooked up my vacuum gauge and the car is pulling 19 in at idle in park, holds very steady. Also took the Mity-Vac to all the lines, EGR, FPR and everything holds fine. Almost positive there is no vacuum leak. Cleaned the grounds and checked the battery cables, helped a bit but problem is still there. Also swapped in my known good MAF and no change. Plug wires are AC delco, as are the plugs, coils ohms out ok. There isnt a miss, it just stumbles when it comes back down to idle then goes back to idling smoothly. Figured it had to be something with the IAC so I took it out again, cleaned the passages and reset. No change.