350 tbi idle shaking

[JPVortex]

Hey yall, having a problem on my 94 K1500 with a 350 tbi in it.

Engine runs totally fine in park and has the power it should while driving. However when at or near idle in gear not so much. I feel a decent amount of vibration. The biggest problem is when I go to steer the wheel in near idle conditions(like a drive thru). The rpms dip a ton and surge(to like 500rpm) and the truck almost stalls out. This creates a ton of vibration in the cab and its a bother. I do have 35 inch tires.

I feel like this started after I did the intake manifold gaskets about a month ago. Havent had any other problems than this, no leaks at all.

The engine has been timed after the intake gaskets and I checked it again about a week ago.

I did notice my dizzy cap center post was looking a bit rough and uneven. I also dropped the cap a couple of times. I also had to replace 1 spark plug and I used one thats a different material than the rest. Would either of these cause my problem?

Could it be a vacuum leak or something? Bad IAC?

Any comments are appreciated.

 

[k1500 97]

Um. Whats your fuel pressure.

 

[Marauder]

Have you checked the motor mounts?

 

[Schurkey]

1. Verify the "dropped" distributor cap.
2. Spark plugs, even mis-matched by brand or type, don't inherently cause misfire. But defective plugs can cause misfire.
3. I had to replace the intake gaskets on my TBI twice because the gaskets failed over time--a year, more-or-less. If the wrong gaskets were used, or there was a problem with the installation, the gaskets might be causing an air-leak into one or more runners which is magnified at idle and not-so-bad as the throttle is opened.
4. Connect a scan tool, verify ALL the sensors and computer outputs like the IAC and timing advance 'n' EGR. Make sure you don't have a failing TPS, or leaking vacuum hose to the MAP sensor that's creating idle issues.
5. Assure the plug wires are routed correctly--ESPECIALLY 5 and 7. When 5 cross-fires into 7, it'll blow the air-fuel mix in #7 creating problems at idle, and devastation with higher load. Make sure the plug wires aren't defective, cut, abraded, etc.
6. Checking fuel pressure is recommended. Typically isn't an issue at idle, more when the load is higher.
7. Oversized tires are going to make life hell on your PS pump. There's going to be an increased load on the engine driving the PS pump. Doesn't surprise me that this affects the idle speed.

 

[Jjbiskup]

1. Verify the "dropped" distributor cap.
2. Spark plugs, even mis-matched by brand or type, don't inherently cause misfire. But defective plugs can cause misfire.
3. I had to replace the intake gaskets on my TBI twice because the gaskets failed over time--a year, more-or-less. If the wrong gaskets were used, or there was a problem with the installation, the gaskets might be causing an air-leak into one or more runners which is magnified at idle and not-so-bad as the throttle is opened.
4. Connect a scan tool, verify ALL the sensors and computer outputs like the IAC and timing advance 'n' EGR. Make sure you don't have a failing TPS, or leaking vacuum hose to the MAP sensor that's creating idle issues.
5. Assure the plug wires are routed correctly--ESPECIALLY 5 and 7. When 5 cross-fires into 7, it'll blow the air-fuel mix in #7 creating problems at idle, and devastation with higher load. Make sure the plug wires aren't defective, cut, abraded, etc.
6. Checking fuel pressure is recommended. Typically isn't an issue at idle, more when the load is higher.
7. Oversized tires are going to make life hell on your PS pump. There's going to be an increased load on the engine driving the PS pump. Doesn't surprise me that this affects the idle speed.

Number 3 sounds like my problem, might i add that the misfire is random. It also doesnt run super rough but it is still a misfire and i just want to make sure it wont leave me stranded one day, i already replaced the alternator, battery, coil to cap wire lead, spark plugs(ac delco copper as it says in oem spec) And it doesnt run nearly as rough before but it still randomly shakes every now and then in idle.

 

[k1500 97]

Number 3 sounds like my problem, might i add that the misfire is random. It also doesnt run super rough but it is still a misfire and i just want to make sure it wont leave me stranded one day, i already replaced the alternator, battery, coil to cap wire lead, spark plugs(ac delco copper as it says in oem spec) And it doesnt run nearly as rough before but it still randomly shakes every now and then in idle.

My 97 5.7 vortec shakes at idle to, but a little gas clears it up, almost like she has a cam

 

[k1500 97]

N

My 97 5.7 vortec shakes at idle to, but a little gas clears it up, almost like she has a cam

I know that doesent help you, or sound good in my problem also

 

[95 Tahoe]

I have a thread going on a similar problem. Mine is running a bit rich and the vacuum is a bit low. If I find the answer I'll post it.