rfoster23g

So I have a 1992 with a Camaro 5.7l 350 from a truck I believe. So my problem is that my car surges at idle. most of the time it does but sometimes(rarely) it actually stays steady. Basicaly it will not stay steady it just idle up to 1500 then down to 500 untill it stalls or sometimes starts idleing smooth but rarely. I do not know what to do next... So far i have swapped and tried to set the iac, replaced the cts, and map sensor. I can not find any vaccum leaks but i feel if it did have a vac leak why would it sometimes run great and other times surge. If you haven't already guessed im stumped. I have done tons of searches and have so far been inconclusive. I will answer any questions and if I fix this problem I will post my solution to help others in the future

no surge at idle cold
warmed up example of surge
Outside sound of what car is doing
unknown connections under dash and example of car idling perfect after surging stops

will take more videos upon request I am just desperate for a solution to this problem

FlyDoc

retarded timing will take power out, it will help it start though.
*check the break booster to see if it is leaking.
*has the intake been off? maybe its leaking.
*fuel pressure?
*if you have an auto, the vacuum modulator could be bad.
I hate the idea of just throwing parts at a problem not having a clue of what the issue is.
I would suggest getting a malti meter, to test your electrical components and sensors. and a vacuum tester.
hope that helps

rfoster23g

ya im going to try to advance the timing a tad.
I didnt check the brake booster really but i will today.
I sprayed a bunch of starter fluid around all over the place and nothing
i haven't checked the fuel pressure since we kinda ruled it out becuase it runs great sometimes.
its a manual
me to but what can you do

rfoster23g

bump please help any ideas would be greatly appreciated

FlyDoc

has it always ran Like this or is this new?
did you put the "new" motor in or did you get the car this way?
what was the stock engine?

if you got the car with this engine in it, and the factory engine was a 305 then you have a engine / ECU compatibility issues.
need info.

rfoster23g

Well I received the car like this but we messed with the idle screw and I feel we made it worse!!!!!! Its been surging since we got it. It is a different motor I believe it was swapped from a stock 305 tbi to a 350 tbi from a truck (i am guessing though). I will pull the ecu and check the serial codes as soon as it warms up outside(Its in the teens now). I think I am about to go back to the basics first with the fuel pressure need to get another tester did not realize these do not have schrader valves grrrr. I have already replaced the fuel filter no difference. If fuel is not an issue then I will replace ALL vacuum lines. If need be I will just start with a new wiring harness idk what else to do.

rfoster23g

The engine that was in it was originally a 305 tbi paired with a 700r4 (confirmed through rpo deciphering). The car now has a 350 tbi with 14102188 heads assuming from truck from 88-95 (not sure how to identify it further than that) and the transmission is a t5 5 speed now. The car had the axkt chip in it and 305 injectors. With the help of tuned Performance I got my a new chip in the ecu, rebuilt the throttle body put the correct injectors for the 350(brand new, and a new knock sensor. The parts I have replaced are as follows: injectors, knock sensor, map sensor, tps sensor, iac valve, and a new chip. I am not sure what kind of tbi unit is being used since I was under the impression that the 305 and 350 use the same tbi units. I have since replaced the headers and has a complete new exhaust system and while in the process of that I replaced the plugs, wires, cap, button, icm, and coil. The next thing on my list is to replace is the cts, iat sensor, and a heated o2 sensor. I also heard that air in the cooling system can affect idle somehow and I had a radiator leak. So I replaced the radiator, thermostat, and water pump. I am not sure if these are related but I replaced the alternator twice had to warranty the first one so it is less than a week old. The starter is new also so I know the wires down there are good. sorry for not putting enough info up I am happy to put up any more also Thanks Guys

RBob

iTrader: (1)

Fuel pressure checked?

Has any of the above changes made the surging less?

RBob.

rfoster23g

Yes I did check the fuel pressure it read normal around 9.5 to 10.5 (not sure how accurate gauge)

Dens71TA

iTrader: (5)

My '82 T/A with cross-fire TBI was doing something similar. I hooked a GM TECH 1 scanner to the ECM and it was showing a lean condition. Checked fuel pressure and was only around 11 PSI so I adjusted it up to 13 PSI and that fixed the problem.

rfoster23g

would buying one of those adjustable fuel pressure regulators help

RBob

iTrader: (1)

There is something wrong with the fuel pressure. It is within spec, but on the low side. The bad part is that it is fluctuating 10%, it should (needs to be) steady.

What happens to the fuel pressure when the throttle is whacked open?

RBob.

rfoster23g

alright posted up two videos kind of rushed I am running late late for work

RBob

iTrader: (1)

With the 100 psi gauge it is difficult to see if the fuel pressure is moving. It actually looks like it may be. Sometimes it appears to be a little under 10 psi, then at other times slightly above 10 psi. Although, it may be due to the angle of the camera tot he gauge face.

Anyway, there is a slight whistle is the warmed-up video. That is typically a sign that the TBI base gasket is dried out. This is the gasket that goes between the TBI unit and the intake manifold.

RBob.

rfoster23g

Ok I will see if I can get a intake gasket and try to replace it hopefully it's not a big job. Would I be able to reuse the throttle body base gasket

rfoster23g

Are there any tips you all could give me for replacing the gasket

RBob

iTrader: (1)

Not the intake gaskets, but the TBI base gasket. The one under the TBI unit. Easy to replace. If the gasket is dried out and not sticking to either surface, it is a 15 minute job.

Remove the three TBI hold down bolts, slid current gasket out, slide new gasket in, install and torque hold down bolts. Done.

RBob.

rfoster23g

Oh the tbi base gasket is brand new since I rebuilt the tbi unit with new injectors. but the wierd part is I bought the whole gasket set and it came with 3 different base gaskets am I supposed to use both or just one. They were all different styles and only one came out so I put one back in that matched the old one. Could it still be leaking I tried to torque them all the same.

RBob

iTrader: (1)

Just one gasket is used. It may be that that whistle is from the IAC. Can put your finger over the opening on top of the TBI to stop air from flowing through the IAC.

RBob.

rfoster23g

Sorry could not get to the car tonight but I will say upon start up my car has a extreme sucking noise from the tbi unit that when cold is louder than the exhaust... Is this normal?

RBob

iTrader: (1)

Yes, normal. It is that the IAC is open far enough to keep a cold engine running. As the engine warms up the IAC closes down which reduces the airflow past the IAC's pintle.

On a cold idle without the air cleaner the noise from the IAC can be deafening.

RBob.

rfoster23g

It was hard to tell if the whistle went away but I put a piece of plastic in the iac hole and it just stalls the engine. I am not sure but there is a ticking sound almost like a chain when it is idling when warmed up could this be a worn out iming chain you can hear it in the warmed up video of fuel pressure check video. also that is not the fan since there isn't one hooked up.

Joe Tag

iTrader: (4)

One of he first things I do on any SBC is a double roller timing chain. If you have ever seen the nylon on the cam gear wear out and crack off, you would understand why.

rfoster23g

I am completely out of ideas should I just jump for a moates obd1 cable and see if I can datalog with it?

rfoster23g

any ideas on where to head next!

rfoster23g

Would getting a usb to obd1 cable help or would I be wasting my money?? I was thinking I could see exactly what the engine is doing. I also feel like there is almost a miss at idle and I was thinking about replacing the distributer since everything on the ignition side is new

armos

Personally, regardless whether it ended up helping for this problem or not, I'd still want to have the equipment to datalog. It's really nice being able to see what the ECM is seeing and what it's doing. I got spoiled by it. That said, even when you have log data, it can feel like you're chasing your tail trying to figure out what's cause and what's just effect.

Your surging problem is very similar to what my 2.8L Fiero was doing a couple years ago. It only happened after warming up. When datalogging, I could see the short term fuel trim (the INT value) was unstable, it was adjusting for less and less fuel and once it got into an extremely low range it would start to surge. When it saved against a stall, the INT would jump up suddenly and the idle would stabilize. Then the INT would start dropping again and the problem would repeat. Being able to see this helped point to the problem. In my case it turned out to be a subtle tuning issue between the ECM vs the injectors.
That's an obscure thing though, and I don't mean to distract you from simpler explanations as have been suggested.

rfoster23g

Thanks for the input I will definitely invest in getting the obd1 cable. At this point I am trying to just get this thing to be a reliable daily driver

rfoster23g

Ok so I have a little update I had a spare ecu that was for a 305 camaro with a 700r4. I just slapped it in there and it idled beautifully I think a little rich but it seemed to run rich so I am going to swap the chip into this other one just to eliminate it as a culprit.I was reading a article posted up here about the vss not being connected to see if he could get it to run good.THough it had a few side effects like when coming to a stop the car wanted to die. I have figured out that the car really doesn't surge all that much any more it is just when the car is coming to a stop it really dips to 300 then shoots back up to a 1000 or so then smooths out. The forum post said that the vss helped the car maintain the idle and helped control the iac. Anyway the symptoms basically described my problems down to a tee. I remember like two months ago the check engine light would come on and it would throw a vss code could this be one of my problem. I will go read the codes again tomorrow but one thing I know is the transmission was swapped out from a 700r4 to a t5 by one of the previous owners. Just let mo know what you all think.