350 TBI help

99ncxj

99ncxj

Well-Known Member
Joined
Sep 23, 2006
Location
Aliso Viejo, CA
I picked up a 95 K1500 today and its got a tbi 350 in it. It idles fine and cruises fine but it has a hesitation just above idle. If you blip the throttle from a stand still it revs up just a little like it should but then drops back down below normal rpms and almost dies. the PO said he thinks the guy he bought the truck from had put a cam in it but I can't verify that. Any ideas? I'm thinking maybe air leak at throttle body mating surface or maybe a vacuum leak somewhere.
 
I know RickyB knows of this truck, maybe others do too.

ai190.photobucket.com_albums_z249_99ncxj_Chevy_201500_1500.jpg
 
While the engine is running shoot some starting fluid around the throttle body and vacum lines, if there is a leak it'll rev up cause its sucking in the fluid.

Also check the fuel filter, id say just go ahead and replace it

and then yea i'd say just either the throttle body needs pulled apart and rebuilt (very easy, just a few gaskets) or the injectors are just old and starting to fail

fuel pump could also be a culprit, its testable, just a pain in the butt to do it and you gotta have a pressure tester with all the right hookups and what not

start with the fuel filter and starting fluid thing
 
I had a 90' do the same thing & it turned out to be the throttle position sensor. It cheap & easy to change to see.
 
I have seen that truck around. I put my vote in for IAC or TPS. Take the IAC off the TBI and hose it down good with carb cleaner then put it back in. If the stumble goes away that was it. Drive it like that or buy a new IAC.
 
After further "looking" today, I noticed that the truck has a poweraid throttle body spacer and pace setter headers. I also found the rubber vac line going from front of tb to the small black box with wire plug on it was cracked. I replaced it but nothing changed.

I've been told that the larger cam can affect the vacuum on the engine. Might need another vac canister?
 
A hand held propane torch for checking vacuum leaks will keep an under hood fire away.
 
99ncxj said:
After further "looking" today, I noticed that the truck has a poweraid throttle body spacer and pace setter headers. I also found the rubber vac line going from front of tb to the small black box with wire plug on it was cracked. I replaced it but nothing changed.

I've been told that the larger cam can affect the vacuum on the engine. Might need another vac canister?
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If it was that big of a cam you'd know. Damn thing would lope like no tomorrow. Wouldn't hurt to throw a vac gauge on it to see what she's pullin.
 
I don't think its much bigger of a cam over stock. It doesn't lope much unless the idle drops due to...something maybe vacuum related. I'm going to hook up my guage tomorrow and see what its pulling.

The other reason I'm thinking vac could be an issue, is the brake pedal is soft for the first half or so of travel but if you pump it once it is firmer higher up. It feels like the brake booster doesn't have enough vac on it to keep the pedal firm.
 
That sounds like the mc is goin, at a stop when you push on it if it slowy goes to the floor then yeah it's the mc. A bad brake booster makes the pedal pretty hard to do any sort of braking. Sounds your truck is just making a list of problems for you.
 
You guys are throwing out some terms I'm not familiar with. I know what the TPS is but whats the IAC and IWS? I'm hoping to find someone to sell/install a dual in/dual out muffler tomorrow morning. If I keep driving it with these dual straight pipes i'm going to go broke buying goodies powders. Plus the neighborhood is going to end up slashing my tires :D
 
99ncxj said:
You guys are throwing out some terms I'm not familiar with. I know what the TPS is but whats the IAC and IWS?
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IAC= Idle Air Control
IWS=Irregular Warfare Support

Maybe could be a MAP sensor either.. disconnect the TPS and see if it gets worse.. repeat for MAP sensor, and IAC motor.
 
IAC idle air control
IWS I'm with Stupid
 
Update:

I've had the truck for a couple of days now but havnt had time to do any work on it. However, I noticed the last two days that when the engine is still cold, it runs perfect. It only starts doing this mess once it's warmed up.

With that bit of info, I don't see how it could be injectors, tps, or fuel filter related. Anyone else think it may be egr related? I'm going to pull it and clean it out tomorrow.
 
99ncxj said:
Update:

I've had the truck for a couple of days now but havnt had time to do any work on it. However, I noticed the last two days that when the engine is still cold, it runs perfect. It only starts doing this mess once it's warmed up.

With that bit of info, I don't see how it could be injectors, tps, or fuel filter related. Anyone else think it may be egr related? I'm going to pull it and clean it out tomorrow.
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So what you're saying is it has the opposite problem that your other truck had? :lol:
 
no, my old truck had way more issues than this one. Plus, this one will be much easier to sell once these few issues are fixed.
 
Still could be a fuel filter. Its takes a while for the trash to get stirred up (time it takes to warm up). I also vote for an IAC. The egr could have a little to do with it though. Cant hurt to clean both.
 
until it goes closed loop the sensor dont matter much...doesnt go close loop until warm.
 
Ron said:
until it goes closed loop the sensor dont matter much...doesnt go close loop until warm.
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99ncxj said:
It only starts doing this mess once it's warmed up.
Click to expand...

hrm. the sensor is? MAP? TPS works from when you start it, so rule that out probably.. IAC may be it if the motor in it is seized/frozen/stuck/gummed... could be also IATS [Intake Air Temp Sensor] but I don't think they are much subject to going bad..
 
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