1994 hesitation while driving

[ol'blazer]

My truck runs fine at idle and acceleration, but once you're at speed it almost stalls and hesitates once in awhile....what would cause this? the truck rid perfect otherwise, any help would be great!

[Camo]

Originally Posted by ol'blazer

My truck runs fine at idle and acceleration, but once you're at speed it almost stalls and hesitates once in awhile....what would cause this? the truck rid perfect otherwise, any help would be great!

I am having the same problem with my '94.
Free bump I guess.

[rickpilgrim]

Vacumn leaks come to mind first, coolant temp sensor second, weak o2 sensor third and map sensor getting bad also has these effects. If the check engine light is on or you could get codes if any that would help

[Camo]

Originally Posted by rickpilgrim

Vacumn leaks come to mind first, coolant temp sensor second, weak o2 sensor third and map sensor getting bad also has these effects. If the check engine light is on or you could get codes if any that would help

Thanks, I'll suggest those to my mechanic. It happened to me this morning actually and my engine shut off when I tried to take off at the light lol.

[RayInAlaska]

Since there is nothing to lose, I would pour some Seafoam in the gas tank and see how it goes.

[Cabnchassis]

Usually when it stalls on take offs or shifting D to R it's a vacuum leak or failed IAC valve

But it can be any of the following things giving improper information to the ECU and you'll have to trouble shoot each one individually. If you look through my past threads I've written a couple large posts that will explain how to trouble shoot the things I did, everything else was either already new (oxy and MAP in my case) or I just replaced it. For instance I'm not going to bust out my multimeter to make sure a ten year old $15 CTS is any good, I'm just going to replace that type of stuff every time. Honestly most of these things are kind of "wear items" on these motors because the motors tend to last a lot longer than the misc crap bolted to it. Also I had a 454 TBI work truck that pooped the bed (warped the head first day and knew it but the boss said blow that turd up, he wasn't paying to fix it or tow it one more time...) cause of a bad CTS to the gauge so I change them on every vehicle I buy.

CTS sensors
IAC vavle
EGR valve clogged or failed
MAP sensors
OXY sensor
Low fuel pressure--> from weak fuel pump or restriction on the line or within the TB
Vacuum leaks--> usually found at either the TB base gasket or intake manifold gasket, CAN HAPPEN INTERNALLY. Mine was crossed over inside the intake pulling air from a cooling passage and there is no good way to diagnose that unless you verify that all that other stuff is working correctly and seal up every other possible vacuum leak. I literally replaced or troubleshot every other item on the truck to figure that out though.

If you remove the intake manifold DON'T forget that the front of it seals to the block with RTV not a gasket and it's pretty easy to forget to do. Also the dizzy wont go back in without turning the fuel pump with a very large flat head screw driver. The dizzy has a tab on the bottom that fits in the oil pump to drive the pump. When you pull it the oil pump unloads most times.

If you unplug the IAC it will cause the ECU to reset and the truck will run good until the ECU resets to the current operating conditions at which point it will return to running bad. So figure out either first or last of the devices mentioned to do the IAC cause you won't be able to continue trouble shooting after it resets.

Honestly the two most common causes I see in the world and on the forum when they are stalling is either Major Vacuum leak or bad fuel pump.

[ol'blazer]

its not sending any codes, i replaced the 02 sensor less than a year ago, checked the fuel pressure... so would you say the map?

[Cabnchassis]

The MAP sensor is code uppity on these things. Anything causing enough change in manifold pressure either positive or negative and it'll code because of that even if it's nothign to with the MAP at all. I'd check the EGR first. If Money isn't tight on preventive maintenance you can just change them both out cause they will both go at some point during the life of the truck. The MAP is also $50 and won't harmanything if it fails beyond maybe needing a tow which isn't even likely. These engines last through at least one round of the junk hanging off them going bad and a lot of stuff you'll change more than once if you own it for a long time. Lots of these engines go 300k and beyond and most at least pass 200k, most of the ancillary parts just aren't that kind of durable.

This is a good troubleshoot article for these specific EGRs.

[Cabnchassis]

The TPS can cause throttle issues too but idk how to diagnose it.

[ol'blazer]

I pulled the throttle body off and found a ripped gasket, it didn't sound like a vacuum leak. But I think that's my issue

[Cabnchassis]

I'm sure you noticed that well planned bolt spacing and you do want to torque it down even, its easy to make it leak on that long side toward the firewall. If you buy the TB gasket "kit" at the parts house it'll come with the upper and lower TB riser gaskets, but make sure both are installed. They aren't part of your issue but you you can hear a slight difference in how clean it idles. Most of the time the top one that seals the air cleaner is missing bc it falls off when people pull it and they don't notice.