94 K1500 4x4 erratic idle

When I first start it it runs up to idle at 1500rpm then slowely drops. Once warmed up it is where it should be except the idle bounces anywhere from 300 to 1100rpm.
I have installed a new IAC and Throttle Control. I regularly run injector cleaner in every other tank of gas.
I have also noticed at times when i let off the accelerator while moving rapidly it will chug and clunk from somewhere in the middle of the truck underneath, like trany is trying to coast since I let off the gas but then it wants to go and then not and then go until i get slow enough or press back on the gas pedal.
I have put a new fuel pump in a few years back along with filter. I also put in a cooler thermostat when I had to remove the manifold to repair heater hose fitting that corroded off. I have replaced cap/rotar/plugs and wires in the last year too.
It does not stall at all, it comes close but not enough to set off any codes.
Any ideas please help.

When I first start it it runs up to idle at 1500rpm then slowely drops. Once warmed up it is where it should be except the idle bounces anywhere from 300 to 1100rpm.
I have installed a new IAC and Throttle Control. I regularly run injector cleaner in every other tank of gas.
I have also noticed at times when i let off the accelerator while moving rapidly it will chug and clunk from somewhere in the middle of the truck underneath, like trany is trying to coast since I let off the gas but then it wants to go and then not and then go until i get slow enough or press back on the gas pedal.
I have put a new fuel pump in a few years back along with filter. I also put in a cooler thermostat when I had to remove the manifold to repair heater hose fitting that corroded off. I have replaced cap/rotar/plugs and wires in the last year too.
It does not stall at all, it comes close but not enough to set off any codes.
Any ideas please help.
First get the proper 195 stat back in it.
Any codes or check engine light?
Good AC delco plugs and cap?
Have you checked the dist shaft for side play?
Have toy checked the TPS sensor?
How is the fuel filter?
Good hot blue spark out of coil and to all plugs?

When I first start it it runs up to idle at 1500rpm then slowely drops. Once warmed up it is where it should be except the idle bounces anywhere from 300 to 1100rpm.
I have installed a new IAC and Throttle Control. I regularly run injector cleaner in every other tank of gas.
I have also noticed at times when i let off the accelerator while moving rapidly it will chug and clunk from somewhere in the middle of the truck underneath, like trany is trying to coast since I let off the gas but then it wants to go and then not and then go until i get slow enough or press back on the gas pedal.
I have put a new fuel pump in a few years back along with filter. I also put in a cooler thermostat when I had to remove the manifold to repair heater hose fitting that corroded off. I have replaced cap/rotar/plugs and wires in the last year too.
It does not stall at all, it comes close but not enough to set off any codes.
Any ideas please help.

sounds like it starts normal ..then after warming the idle gets wacky.

this can be the egr sticking or a vacuum leak ..intake manifold/pcv crankcase hoses etc.. check vacuum cold then hot see if you loose proper vacuum..use a guage.

replace fuel filter every 30,ooomiles..with a old steel tank with alcohol fuel in the gasoline maybe more often ..

First get the proper 195 stat back in it.
Any codes or check engine light?
Good AC delco plugs and cap?
Have you checked the dist shaft for side play?
Have toy checked the TPS sensor?
How is the fuel filter?
Good hot blue spark out of coil and to all plugs?

No codes that I have noticed. I will get that checked tomorrow to be sure. I replace plugs with factory always and have done last fall along with cap/rotor. Fuel filter last year. TPS 3 months ago when I had to pull intake to repair corroded water fitting on manifold that fell apart. Yesterday I rebuilt the TB and replaced a cracked boot to valve cover from back of TB. The only thing I changed from factory was the T-stat. Distributor looked good when we had it out. We timed it at 0 using the wires under the dash as specified.

Ran perfect for 2 months. 2 years ago I put a new fuel pump. It runs on all 8 cylinders fine especially when moving. I notice it most when parked or at a stop, it just wants to idle erratically. Lurch forward or nearly die. Some days are worse than others. Sometimes if i re-start it after a short drive its is better. Seems to prefer warm days over cold/cool ones.

I have done nothing with the coil ever, I will have to look at that. I figure the coil wouldnt act like this, it would just quit all together?

It almost acts like its about to idle down and die then it reacts and saves itself to just do it over and over again.

Wanted to mention the TPS I replaced twice. The first one didnt work at all. Took it back and exchanged it for another. Wonder if it was made in CHINA and is garbage.

Also when I replaced manifold the gasket kits no longer come with end seals, just silcone. What if the silicone didnt fill in everywhere, could that cause it if it blew out?

I miss the old stuff that was easy to figure out without process of elimination! Id love to rip out the electronic crap and throw on a Holley and a mechanical fuel pump on if that would be easy but Im sure theres a lot more to it than just that.

No codes that I have noticed. I will get that checked tomorrow to be sure. I replace plugs with factory always and have done last fall along with cap/rotor. Fuel filter last year. TPS 3 months ago when I had to pull intake to repair corroded water fitting on manifold that fell apart. Yesterday I rebuilt the TB and replaced a cracked boot to valve cover from back of TB. The only thing I changed from factory was the T-stat. Distributor looked good when we had it out. We timed it at 0 using the wires under the dash as specified.

Ran perfect for 2 months. 2 years ago I put a new fuel pump. It runs on all 8 cylinders fine especially when moving. I notice it most when parked or at a stop, it just wants to idle erratically. Lurch forward or nearly die. Some days are worse than others. Sometimes if i re-start it after a short drive its is better. Seems to prefer warm days over cold/cool ones.

I have done nothing with the coil ever, I will have to look at that. I figure the coil wouldnt act like this, it would just quit all together?

It almost acts like its about to idle down and die then it reacts and saves itself to just do it over and over again.

Wanted to mention the TPS I replaced twice. The first one didnt work at all. Took it back and exchanged it for another. Wonder if it was made in CHINA and is garbage.

Also when I replaced manifold the gasket kits no longer come with end seals, just silcone. What if the silicone didnt fill in everywhere, could that cause it if it blew out?

I miss the old stuff that was easy to figure out without process of elimination! Id love to rip out the electronic crap and throw on a Holley and a mechanical fuel pump on if that would be easy but Im sure theres a lot more to it than just that.

You need to get the proper 195 stat back in it.

Check fuel pressure for up to specs.
Check for present/stored/history codes and read out sensor data with a engine capable scanner.

And as J-Cat said run a vacumn check hot and cold engine.
Also check engine vacum at idle and at 2K rpm.

Piost back vacumn and fuel pressure readings and amny stiored history or past or present codes and if all sensor reading to computer are good.

ok. unfortunately I dont have the equiptment to check any electrical/vacuum on this vehicle. I have had 2 codes since. The first was for rich exhaust.

I checked o2 sensor. I rebuilt TB and put in a new IAC. Better for a day then back to the usual after that. No codes for couple weeks.

The second code was for EGR. I tested EGR but without vacuum pump. Instead I pushed in on the back of the EGR and idle got better in neutral and unplugged from EGR, so I replaced the EVR silenoid. Better for a day then back to usual.

Today I ran it with hose off the EGR and it ran smooth but at a higher RPM at Idle(1600) and a little higher then normal when in gear(1000), could feel it pulling a bit.

My next plan is to put 195 stat in it. If still doing it then I am going to replace EGR.

Fuel is spraying nicely/evenly.

I am thinking its the EGR but will first try the stat next, then EGR and will post back.

ok. unfortunately I dont have the equiptment to check any electrical/vacuum on this vehicle. I have had 2 codes since. The first was for rich exhaust.

I checked o2 sensor. I rebuilt TB and put in a new IAC. Better for a day then back to the usual after that. No codes for couple weeks.

The second code was for EGR. I tested EGR but without vacuum pump. Instead I pushed in on the back of the EGR and idle got better in neutral and unplugged from EGR, so I replaced the EVR silenoid. Better for a day then back to usual.

Today I ran it with hose off the EGR and it ran smooth but at a higher RPM at Idle(1600) and a little higher then normal when in gear(1000), could feel it pulling a bit.

My next plan is to put 195 stat in it. If still doing it then I am going to replace EGR.

Fuel is spraying nicely/evenly.

I am thinking its the EGR but will first try the stat next, then EGR and will post back.


if you have no test equipment how did you do the O2 sensor ?

the vacuum guage is / can be very cheap to purchase. with the proper use and knowledge this reveals much about the engines failures.

what codes did you get ? I can tell you with those idle speeds the tranny will not last very long.

remove the EGR and put a plate over the EGR mounting surface , with a gasket ..then see how it runs ...make sure the vac line to egr is plugged.

your not testing/no results my "guess" is engine is running too rich with what little you have revealed.

You can rent or buy or borrow test equipment at parts places.
A lot cheaper than throwing parts at it without proper testing.
As said a vacuum gage is one of the cheapest and most helpful thing you can have that tell you a lot about how your engine is running.
Shows slow timing and low vacuum and engine miss and plugged exhaust and egr valve problem.
Posting back code no would help the people trying to help you.

FIRST CODE WAS A 22, THEN A 45, LAST ONE WAS 32.

I just took off and looked at o2 sensor and it looked clean and in very good condition.

I dont have a problem throwing money on parts, but I do have a problem throwing thousands at it in a shop and they do same process of elimination even with equiptment. I will look into a vacuum. Had this happen on a hesitation on a mercury villager. Dealer took alot of my money for very little and still had problem they couldnt solve.
Thanks for your help

FIRST CODE WAS A 22, THEN A 45, LAST ONE WAS 32.

I just took off and looked at o2 sensor and it looked clean and in very good condition.

I dont have a problem throwing money on parts, but I do have a problem throwing thousands at it in a shop and they do same process of elimination even with equiptment. I will look into a vacuum. Had this happen on a hesitation on a mercury villager. Dealer took alot of my money for very little and still had problem they couldnt solve.
Thanks for your help

WELL IF YOU HAVE THE MONEY KEEP THROWING PARTS AT IT AND YOU MAY GET LUCKIE AND FIX IT.
OR YOU CAN DO A LITTLE PROPER TESTING AND GET RIGHT TO THE PROBLEM.

Code 22 is tps problem.
Code 32 is egr valve or solenoid problem or vacumn problem
Code 45 is rich exhaust.
Just looking at sensor will not tell you much.
But or even with a code proper testing must be done to find problem and fix it.
Good luck

FIRST CODE WAS A 22, THEN A 45, LAST ONE WAS 32.

I just took off and looked at o2 sensor and it looked clean and in very good condition.

I dont have a problem throwing money on parts, but I do have a problem .
Thanks for your help


this is now much better if you want to do this properly.
the TPS is defective or not properly adjusted. at idle the voltage output of the tps should be .4 volts...If not the idle will be commanded high by the ecm....this will create a 2.5 volt signal ..

no voltage the idle would be zero the higher the voltage the higher the idle ! could also be shorted wires/connector/ecm defective.

the O2 sensors can not be looked at with your eyes but with a meter when instaled and the engine is running for a very basic test..to do this best you would need the proper scanner equipment to see the rapid changes in voltage..as it swings above and below the .5volt output.

most times these need replacement at 100,ooo mi as they loose their proper operation which causes more fuel consumption but may not throw codes...manufactures recommend replacement at this mileage....

with coolant injestion of the engine the life of these is reduced very quickly.

my opinion on all this DIY auto repair..

buying a manual for your vehicle,having the basic proper tools to keep your vehicle properly tuned BEFORE SHIT HAPPENS is the cheapest way to go.... In the long run when you own older vehicles or if your are like me , and keep them for a decade or two . never bring an old vehicle to the dealership very costly and in most cases very poor results..\\DEALERSHIPS MAKE MONEY IN CAR SALES NOT REPAIRS .........