1995 Silverado: Rough, Surging Idle and Poor Throttle Responce

[Newell_89]

Alright so here's my problems guys. I have a 1995 Silverado that had a 305 in it but i swapped it out/ replaced with a built 383. It starts but its runs incredibly rough, and there is a delay in throttle response. Its set to idle at 1000rpms and it does but just barley. Most of the time it is bouncing from 800-950rpms then settling at 1000rpms for a few seconds. And it always stalls eventually at idle if i don't intervene by playing with the throttle slightly. If i rev it up to 3500RPM+ it runs smooth and flawless.

I Have a new IAC, TPS, O2 sensor and Distributor Cap.
I checked my hoses for vacuum leaks and can't seem to find any, but i heard a leaky intake manifold gasket could cause such a problem? I have a spare set and am going to replace them(can't hurt+needs to be done when i port match the manifold bores to throttle body). I also heard bad grounds could give you this issue at low throttle or idle? Any way i have a new rotor and plug wires on they're way. I'll update this thread when i get them in and installed.

This is really pissing me off. i don't have anymore money to throw at this. I'm sure its something simple but i just don't know... Ive read a few threads on this sort of problem but none are conclusive, except one i can recall which was because of a faulty knock sensor.

I don't have an OBD1 code reader, but ill have to get one i guess because the check engine light is certainly on.

Any helps appreciated, Ill respond to questions as fast as i can.

[2000CAYukon]

What is the timing set at?

It would help to know what the sensors are reporting and what the fuel trims are at; otherwise, you are just guessing. Might be worth the money to get a scanner hooked up to it.

Make sure the MAP is hooked up properly to the rear of the TBI and that the port is not clogged.

//2000CAYukon

[Newell_89]

Originally Posted by 2000CAYukon

What is the timing set at?

It would help to know what the sensors are reporting and what the fuel trims are at; otherwise, you are just guessing. Might be worth the money to get a scanner hooked up to it.

Make sure the MAP is hooked up properly to the rear of the TBI and that the port is not clogged.

//2000CAYukon

True, ill buy one in a few days. 0 degrees like it says on the fan shroud. And yeah I've made sure its connected properly, and its not plugged.

[2000CAYukon]

Originally Posted by Newell_89

True, ill buy one in a few days. 0 degrees like it says on the fan shroud. And yeah I've made sure its connected properly, and its not plugged.

0 degrees with the EST disconnected, right? Have you tried playing with the timing to see if you can find a spot where it run better at idle and off idle?

//2000CAYukon

[j cAT]

you have not explained where,what,how the replacement engine came into being..

plugs wires good and routed correctly..compression pressure check,vacuum intake ....

timing off will not cause a rough idle,,,poor incorrect spark/poor compression will.....what is the fuel delievery system used...pressure of fuel/leak down ?

defective distributor bearing..

why was the 305 scrapped ?

[Newell_89]

Originally Posted by 2000CAYukon

0 degrees with the EST disconnected, right? Have you tried playing with the timing to see if you can find a spot where it run better at idle and off idle?

//2000CAYukon

Yes, disconected. And haven't really noticed a difference advancing the ignition or retarding it.

[Newell_89]

Originally Posted by j cAT

you have not explained where,what,how the replacement engine came into being..

plugs wires good and routed correctly..compression pressure check,vacuum intake ....

timing off will not cause a rough idle,,,poor incorrect spark/poor compression will.....what is the fuel delievery system used...pressure of fuel/leak down ?

defective distributor bearing..

why was the 305 scrapped ?

The 305 I had in it was a great engine, it served it's time with almost 400,000 km . I swapped it because it was tired. bad compression and burning oil, egr ports plugged solid. I still have it and rebuilding it.

The new engine came to be after I found a replacent 350, and I decided I wanted a deceivingly strong tbi engine so I put together a 383 with some vortec heads and a GM performance parts vortec tbi intake manifold w/egr. It has a mild cam (computer friendly) and a custom burnt chip from Brian @TBIChips.com. It's nothing wild and has been done time and time again. My camshaft is a retro fit hydraulic roller with 1.6 roller rockers. And I know I installed it rite. I have 255lph wallbro fuel pump sending gas too 80ibs/hr bigblock injectors and a bored out throttle body with and AFPR (in line fuel filter is brand new)

I'm going to check compression/vac tommorow or as soon as i get a chance.

How do I check for a worn dist bearing? "play" in the shaft?

Thanks for the input guys, I'll keep you updated.

[Newell_89]

Alright my compression gauge doesn't have the adapter i need to thread into my engines spark-plug locations. i ordered one, it'll be a few days untill i update again with compression results.

[2000CAYukon]

What fuel pressure do you have at idle? Have you tried lowering the fuel pressure? You really need to understand what the fuel trims are especially at idle and off idle.

Is the cam installed advanced, retarded or straight up?

//2000CAYukon

[Newell_89]

Originally Posted by 2000CAYukon

What fuel pressure do you have at idle? Have you tried lowering the fuel pressure? You really need to understand what the fuel trims are especially at idle and off idle.

Is the cam installed advanced, retarded or straight up?

//2000CAYukon

It's set @ 20psi now. But it's running the same way it did at 15psi when I first started it. Everything I've read says I need the higher fuel pressure. But I relize it'll run rich at idle not like shit though. As for fuel trim that is the rate at which the injectors pulse or open and close? How do I monitor the fuel trims? With some kind of datalogging software?

[tblake]

Was your computer tuned to run big block injectors?

[Newell_89]

Originally Posted by tblake

Was your computer tuned to run big block injectors?

It should be, that's what I asked for on the orderform. And the guy that does the chips has a good rep. The order form is pretty extensive with every upgrade required.

[Newell_89]

Originally Posted by tblake

Was your computer tuned to run big block injectors?

Well it should be. That's what I filled out on the orderform and the guy has a good rep for his "know-how".

[2000CAYukon]

Originally Posted by Newell_89

It's set @ 20psi now. But it's running the same way it did at 15psi when I first started it. Everything I've read says I need the higher fuel pressure. But I relize it'll run rich at idle not like shit though. As for fuel trim that is the rate at which the injectors pulse or open and close? How do I monitor the fuel trims? With some kind of datalogging software?

You need a scan tool or data logging software.

See http://carprogrammer.com/Z28/PCM/FAQ...on%20Works.htm

I use WinALDL on a PC with a Cable but there are others.

//2000CAYukon

[Newell_89]

Guys thanks for all your help and input. Especially your time. But it wasnt computer related, a vacuum leak, sensor problem or a fuel problem. It was a "mechanical error" in the valve train. The set of $450.00 Retro-fit Hydraulic Roller Lifters form comp cams had 1 lifter! out 16 that was assembled wrong.. the plunger in the lifter would bottom out in the lifter almost a 1/4" before the rest of them did after setting the valves meaning that my intake valve was staying slightly open. through all 4 strokes.

Only reason i caught this was because i have a dual plain intake and fuel was shooting out of the drivers side cylinder bank side of the throttle body, took the valve covers off to investigate and confirmed my problem. I searched the internet and I'm not the first that had this problem from comp and their retro hydraulic roller lifters.

Anyways just thought i'd let you all know. i dont know how i dident catch this the first time i set the valves, Atleast i know now..