Drop in Idle and/or stall when gas released

okay....I suspect the throttle position sensor has gone off~ https://www.google.com/#q=1989+Chevrolet+C%2FK+1500+throttle+positio n+sensor

Your idle air control valve is either dirty or faulty.

the problem is there are lots of possibilities. Dont go replaceing things randomly, have them tested. Possible thins are: TPS, IAC, vacuum leak, fuel pressure regulator, bad injector, worst case scenario the pcm has messed up. You have already taken care of basic tune up items so thankfully that is out of the equation. I have a love hate relationship with the gm TBI engines. I love the reliability but most problems have the same symptoms and its impossible to just look at it and replace one thing, You gotta test components

My 95 X-71 305 engine is doing just about the same thing I've replaced every sensor u can think of but as long. As your going down the hwy it runs good so null not one person on this site can give me any insight on what it is so good luck.

Having same issue. Replaced map sensor, cts, egr valve and accuator, basic tune up including rotor, cap, wires and plugs. Checked both sides of plugs after running for 2,000 miles. Both sides were chocolate brown. Cleaned iacv and it looked damm near new. I'm thinking it might be a bad wire harrness. Connectors are a little rough. Don't have a wire tester to check voltages.

try replacing the TBI gasket and go from there.

I had same problem check EGR valve and check for vacuum leaks with carb cleaner around base of throttle body listen for idle drop around vacuum lines.

same problem.. ran perfect after a basic tune up( pugs wires cap roar ect. variables for me... i got a new catalytic converter and a muffler( flow master and a magna flow... now it s idle is so low it stalls. and doesn't seem to have the power it used too.

Fuel pump, test the psi on your pump might be low

Where do I start ... I had to gut my cat n now it runs super rich idles like shit after it warms up oh n with a 195 thermos that I've changed out twice it won't run but only 160 deg tops eats has at about 8 miles a gallon .. Only 108k miles on a 94 k1500 no oil leaks but is using oil like it's going out the pan with no plug ... I know my way around this truck n I've replaced n checked damn near everything pcv vacumme lines gutted cat which was clogged next is compression test n plugs again ... Anyone wanna buy this I ve got a shit ton of money in it I'm just over it ... $6000 in just the frame down I've spent ... B d s lift n all no cheap parts and done right .. Tons of pics of the work being done .. Therteast@yahoo.com...

I'm having the same problem and everything I've looked up has mentioned an actuator. That the air to fuel ratio is off due to a dirty or malfunctioning actuator. So I'm just gonna have my mechanic check that. Also I'm pretty sure I have to replace seals (they're still factory parts) and I know I have an oil leak. Fun times.

PVC valve

I have a 1989 v3500 chev crew cab with a 454. Started stumbling at low throttle, stalling when I came to a stop or any low rpm activity. Checked for vaccuum leaks, reset base idle, tested sensor components, ran Win aldl diagnostics, could not get it to run right. Took it to a friend at a local shop and it turned out to be the PCV valve the only thing I had not checked. They replaced it and bata bing bata boom problem solved. I am a pretty seasoned car guy so my point is don’t forget to check the simplest things first!!

Check the timing that was my problem

My 89 Chevy Silverado would not idle after a cold start I took the PCV valve out and sprayed it with carburetor cleaner....no more problems!!!

One of the MOST overlooked parts of these TBI engines is the distributor pickup coil. It's a component of the distributor which plugs in to the ignition module, the same module that sticks out the side bottom of the cap that the coil also plugs in to. In order to change these, you have to completely removed the distributor and completely disassemble the distributor to get the pickup off and replace it. These components are very sensitive and when failing, will cause misfire, idle issues, and cause it to burn rich as well. 11 out of 12 issues like this are because of this pickup coil. Pcv valve cleaning is general maintenance.

CHECK THE DISTRIBUTOR TIMING!! I have a 95 k1500 5.7L. Same issues as described in most of these posts. My egr valve is working fine, tps sensor is new(helped a little), checked and cleaned the IAC sensor. In short, everything is working as it should EXCEPT for the stutter and stall when going full or almost full throttle. I discovered that my distributor timing was slightly off. There is a 9/16 nut on a bracket that holds the distributor in place. It's not very accessible, but it's on the front right underneath the distributor cap. I used a crows foot to loosen it. Then slightly turn it left or right while its running. I went back and forth a few times before I got it right. After each turn either way I pushed the pedal to the floor until it stopped stalling out. Still have a very slight stutter off the line, but other than that, she's running great. I hope this helps someone !! Good luck

Agree with distributor timing. My timing was too advanced. Backed it off a bit and viola. No more sputtering to back up in my steep driveway to put the boat in the garage. The other item I have found is that this ignition is brutal on coil wires. Try replacing that.

Man everybody on here describes my truck problem but everyone has a different answer. So wtf do a good ole boy do? I be like who be right? So I guess I just start replacing parts one at a time.

Listen, and I CAN'T STRESS THIS ENOUGH.... 99% of all these symptoms comes FROM WORN DISTRIBUTOR COMPONENTS...such as distributor pickup coil, which cannot even be seen unless the distributor is completely disassembled!! The other option is go through with a voltimeter and check resistance and what not of all other electrical components, along with the wires and grounds. Keep in mind bad insulation on a wire or a corroded ground will give bad resistance readings to the computer, simple as it is on these TBI engines. Fact is, it could be multiple possibilities as to why it runs like poop...start by LOOKING at grounds and wire insulation, it's the easiest thing to do. Then if that looks okay, start with the most common failed components, like the distributor pickup coil which costs about $15-20 depending on where you get it. It took me a couple days to track mine down, but after everything else checked out, I pulled the distributor and checked resistance on pickup coil (which even LOOKED burnt lol) and it was WAY off. That's what solved my issue. Be certain to clean the hell out of the distributor, especially the advance/retard rotor on top. If it's sticky and doesn't move freely, the distributor is basically stuck in time where you set it. ALSO, if you have a scan tool with pre-96 hookups, these will actually give you real time readings of most components, including O2 sensor readings, ignition advance/retard, iat position, etc, which will help with the diagnostic. Been doing this a little over 3 decades. Hope I helped at least a little lol Happy wrenching!!

i have the same problem 81 Camaro. i'm starting to think my torque converter is locking up

So i have a 1990 C1500 with the 5.7 tbi i have about $1,500 in this dang thing just in parts still not right, it has entire new distributor, cap, rotor, coil, spark plugs/wires, new temperature control sensors, map sensor, throttle position sensor, throttle body was rebuilt, new fuel filter, new fuel pump and screen, cleaned fuel lines, cleaned fuel tank, replaced distributor a second time first was faulty, new thermostat, new ecm, checked relays, checked, fuses, new timing chain, and im sure theres more im forgetting same problem tho really rough idle unless you hold throttle above 1,500 and when you put it in gear it almost dies, it has no power from 0 to roughly 28 mph and even backfires sometimes aftee 28 runs like a banshee and sounds really good im lost need some help bout to set this girl on fire lol

oh yeh and i also had dealership time it and program ecm

EGR? Vacuum hoses/lines? Wire insulation (especially in hot, dry areas)?? Check all that? Sticky EGR can cause that... Dry rotted vacuum hoses... Cracked insulation on the wiring ANYWHERE under the hood... Listen, it's a bitch. It's an old vehicle, things don't last forever especially rubber n plastic. Always start with the basics cause poor hosing or wiring can cause any electrical component to not function as intended, ie getting bad readings cause signals are being lost "in transit" to components due to loss of energy through bad wiring insulation. Gotta love old cars/trucks lol

Burghman412 thank you, yes on the vacuum lines any hoses i could i made new ones replaced ones i couldn't make i replaced with ac delco new lines, new egr valve, and tested its working have checked for vacuum leaks, ive checked the ground wires off a schematic i found online nothing i did changed anything haven't checked other wiring besides looking for obvious stuff, there are only two sensors left to replace the knock sensor and oil pressure sending unit can any of those cause that?

Lmao the good old knock sensor... My sincerest apologies, that one particular component slipped by in every comment posted... Yes indeed, the knock sensor is vital as it detects vibrations that come from a knock, or bad combustion being rich or lean, and is read by the engine computer to adjust timing accordingly. Usually you'll get an engine light if it's bad or there's a bad signal of some sort, but not always. Mine was good, but the lead and wire had to be replaced. Listen, aftermarket wiring harnesses are available for all these trucks, and they're mostly inexpensive cause there's really not that much there at all. In the end I did a complete resto under the hood of mine. Wires were so brittle and connectors were mostly all corroded or bad so I just did the whole wire harness swap. Took only a couple hours and the harness was under $100 from summit

Awesome thank you

I have a 95 sidekick has no throtol at all will idea fine need help

Throttle position sensor

Have your distributor checked. Mine was doing the same thing. I had to replace my distributor

I have replaced literally EVERYTHING related to this problem. IAC, EGR, TPS, Fuel pressure regulator, Fuel pump, Fuel filter, PCV, Spark Plugs, Spark Plug Wires, Distributor Cap and Rotor, Vacuum lines and O2 Sensor. I have spent over $500 throwing parts at it including the ECM and it still doesn't idle worth a crap. I've had it I am pulling the entire fuel injection system off and throwing it in the trash where it belongs and putting a Holley carb on. The intake manifold to swap it over was only $164 (new) and I picked up 2 Holley square bore carbs for $85 (needed rebuilding but kits are only $32). It's what I should've done in the first place instead of blowing money on parts that don't even fix the problem. You would think with all the sensors and crap that they put on, it would be easier to find the problem and fix it, but it's not. I can diagnose and fix a carbureted engine in an afternoon. I have spent months and a have a couple of actual licensed mechanics (not parts changers) scratching their heads.

Has anybody diagnosed the pickup coil (located inside the distributor around the shaft, which has to be removed to get the pickup coil out) or the ignition module or knock sensor?? The pickup coil inside the distributor is one of the most overlooked pieces of the distributor. It plugs into the ignition module. Make certain THOSE wires are not dry rotted or brittle either. Replacing the cap and rotor and wires n plugs n all that won't do squat if you have bad distributor components.

Ok burghman412. How do you suggest I get the "Knock Sensor" out without removing the engine or cutting a hole in my firewall? The "Geniuses" (I say sarcastically) at GM decided to put it on the back of the head between the head and firewall. I can't even get my hand in there to take the plug off much less getting a wrench in there to loosen it to take it off. It makes a hell of a lot of sense putting a part that will go out in a location that is completely inaccessible.

I am rebuilding a 1989 k1500 right now. The engine is completly gone through and rebuilt. I rebuilt the tbi with all new components from the standard kit and it has all new wires and sensors...every single component is new...even the entire distributor. I started it and it did the same thing as you describe. Rough idle and even stalling. Timing was dead on and everything is brand shiny new. I scratched bald spots on my head trying to figure it out and finally started watching the injector spray pattern. It turns out it was the metering spring in the throttle body. They do not come in the standard throttle body rebuild kit. Repair manuals even say to not replace or mess with it. Anyways, I replaced it and problem solved. If the spring or diaphragm go bad, the the fuel pressure drops and increases sporadically. I am not saying that is the problem, but its something to look out for.

Thumper4693 have you figured your issue out? The knock sensor on my 88 chevy k1500 5.7 is on the passenger side in between rear openings of exhaust manifold. I am able to get to it from underneath.