Dragster Racer

When the car is in park the idle is around 600 at operating temp. Idle is solid at 600 and if I hit the throttle and let rpms drop fast they come right now and goes back to 600 with no fluctuation. Car drives good, no hesitation or any issues under throttle.

When the car is put into gear the idle drops to around 500 but it will sometimes drop down to 300-400 when first put into gear and then it corrects itself and settles back around 500. Same thing happens when coming to stop sign. When you stop with car in gear the rpm will drop low 300-400 and recover before settling around 500. TPS sensor voltage reads good at idle and all the way through full throttle so it is fine. What would cause the idle to drop low when put into gear or coming to stop and take a second or two to settle around 500?

Doesnt throw any codes. Fuel pressure is good. 42 psi with key turned on and 36 psi running. Still have a pressure drop issue when car is turned off. Replaced FPR. Might have a leaky injector. Could a leaky injector cause this issue?

ploegi

Slow, or sticking IAC.

Dragster Racer

Would this only effect idle in gear and not in park? Like I said in park it idles great and snaps right back to idle after revving. Its only when in gear it does this.

Dragster Racer

Well was a long day. Not sure I went forward. Installed new injectors from Southbay. Installed new IAC from AC Delco. Fuel pressure loss problem when key pump turns off didnt change so no leaky injectors. These Southbay injectors tick. Never heard that before. Anyway started it and it would run with gas pedal opened but wouldnt idle at all. Checked things. Took it apart and put it back together and still no idle. Put old IAC back in and it went back to running just like before. Starts up and idles just fine. Once it warms up idle drops down to 600. Put it in gear and it drops and hunts a bit. 300-500. Could I have gotten a bad IAC since the new one wouldnt idle at all? I did the reset for IAC. Turned key on and unplugged IAC, turned key off and plugged back in but nothing with new one.

After I ran it a while I turned it off and was working the garage and about 5 min later I hear a hissing sound. I check and it appears to be form the fitting at the back of the rail where the line goes to the cold start injector. Bad o-ring? Never did that before.

Anther thing it didnt do before today was throw codes 34 and 44. Seems like I am going backwards.

Is it possible I got a bad IAC or is there something else I needed to do to get it to work? Where could my fuel pressure be dropping to? I cant find any leaks and pressure drops fast when pump stops. Changed FRP, IAC(didnt work), injectors.

Tuned Performance

iTrader: (92)

https://m.autozone.com/fuel-delivery...96537&cmpid=cj

You might want to start with the code 34 , you could be fighting a bad ecm.
As far as the idle issue goes.
Does the new iac make a ratcheting noise when command in ? (Jumper the aldl a to b)
http://chevythunder.com/maf_code_34.htm
Do you recall when the pump was installed was the pulsator deleted ?

Dragster Racer

I dont think its a bad ecm cause the old IAC worked and it worked again when reinstalled. The couldnt tell you if new one made any noises as I couldnt leave the driver seat of it would die istantly with new one installed. The code 34 never existed before I installed the new injectors so it seems that I am going backward with these changes. Still dont understand why the fuel pressure drops after pump turns off. No new fuel pump has been installed and nothing us deleted. Pressures read fine when pump is running and car is running.

GeneralDisorder

iTrader: (1)

Get some live data - check the MAF voltage against the table in the ROM for airflow grams per second. Idle should be around 5.0 grams per second for a 500 RPM idle.

The Bosch III injectors do make ticking noises - it's just their nature, and when used in a batch fire configuration, all 8 injectors fire at the same time adding up to a pretty significant tick noise. But this is "normal" for them.

Idle speed being too low could be a lot of things - the ECU may be trying to help you with that code 34. It is one of the most common failures on the MAF cars. The MAF's themselves weren't the most reliable part. That's why a lot of us have gone to speed density.

GD

Dragster Racer

Finally!!!! Found a big vacuum leak on the cold start injector. Fixed that and it runs perfect. Idles in park and in drive. Idles perfect when you come to a stop sign now. It still threw a 34 and 44 code so not sure if everything is still adjusting to the new injectors. It never threw those codes before I changed injectors. If it keeps throwing those codes Ill do some checking.

Dragster Racer

How do I get live data? Do I need to take it to a GM dealer or who has the devices that hook up to these old connectors and systems? You say all fuel injectors fire at the same time? So the connectors are specific to the injector? I thought the injectors fired as needed for each cylinder......

Tuned Performance

iTrader: (92)

The injectors fire in batch not sequential.
you can use tunerpro rt and a moates.net xtreme aldl cable get data from the ecm.
your ecm mask is $32 you might have to convert tuner pros ads to adx or use winaldl.

Dragster Racer

Are there other causes for a code 34 and 44 besides a bad MAF and O2 sensors? I was not getting either of these codes before I installed new injectors and IAC. It seems odd to me these two sensors would suddenly fail the same time as new injectors and IAC are installed. Why would installing new injectors cause these codes? It runs great now but starts way harder than it did before new injectors and IAC valve. One step forward two steps back it seems,

Dragster Racer

I think I found the source of my hard start issue. To confirm is was a fuel starvation causing the problem, I sprayed some carb cleaner in through the throttle body and it started right up instead of the normal long cranking. Next was to troubleshoot my fuel pressure bleed off problem. I pinched off the feed gas line after fuel pump stopped and it slowly bleed down instead of dropping like a rock. This would mean the check valve in the fuel pump is bad, correct? I am getting 42 psi when key is turned on but bleeds to 0 in a few seconds after the pump stops. What doesnt make sense to me though is when I watch the fuel pressure while trying to start the engine the fuel pressure shows 40-42 psi but still hard starts. Is this cause there is air in the line? If the pressure bleeds down does that mean there is air in the line and I will still show pressure even without complete fuel filling the rail when the pump kicks on?

Once the engine starts though it seems to run and idle fine. It has been throwing a 44 lean code after driving for about 10-15 minutes. I can get it to go off if I open up the throttle for a bit. It seems to throw it more around town then on the highway. All this seems to point to a vacuum leak but I have sprayed carb cleaner on every hose, fitting and plenum connection with not leak found. Could a weak fuel pump cause this problem? Meaning it still show pressure but not delivering the volume? Under engine load and higher rpm the pressure should be worse in this case and throws the 44 code more with no load and doesnt under load.

ploegi

Is your cold start injector working? The 'spray carb cleaner and it starts right up' would indicate that , no, it isn't working.....

Dragster Racer

I wouldnt rule it out but have a few questions. Does the cold start injector always come on cold or hot engine? It hard starts in both conditions. Would the fuel pressure bleeding off back through the feed line cause air in the systems? How would I test the cold start injector to see if it is working? If I pull it out and crank engine if it is working wont it spray fuel all over?

ploegi

Yeah, on a cold motor, (not sure what temp the ecm decides it doesn't need it....) it *should* spray fuel. Don't recall if the engine needs to be turning for it to spray though.

Tuned Performance

iTrader: (92)

Post 2 has csi testing
https://www.thirdgen.org/forums/tech...atic-only.html

Dragster Racer

I pulled the CSI out and cranked engine a couple times. CSI is spraying fuel so that's not it. I still think its a fuel shortage issue. When engine was warm, so no CSI engagement, it hard starts. After driving 10-15 min it throws a code 44 lean. I have sprayed carb cleaner in every connection I can find and no leaks detected. Brand new Southbay injectors installed so I dont think they are the problem. When it was cold I cycled the key on a couple times before trying to start and it started right up. When I look at fuel pressure it reads 42 when key is turned on so I am stumped.

If I go out and turn key stoned cold it hard starts. If I try to start warm it hard starts. It its cold and I cycle the key a few times it seems to start better. Throws code 44 lean after driving a while. Thats what I know.

I also check resistance on ECT sensor and it read right.

ploegi

How old are your plugs?? What brand? Heat Range?