My money is on the IAC motor or the EGR control solonoid(not the valve itself) I tried cleaning my iac didn't help, went to autozone picked one up for like 25 bucks put it in and it idled just fine after that.
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.
Thinking of doing the unthinkable... *Rotor to cap gap. Normal?*
- Thread starter y5mgisi
- Start date
Just for the record and/or future reference. When the O2 cools down on my motor while idling it freaks out idle goes all over the place for as long as 5 or 6 minutes, then it'll kick into open loop for 30 seconds or so then go back into closed loop and start all over again. granted I have headers and it's way cold here right now, but it that's what they do, have seen it happen with a weak sensor and poor grounds.
This is purely speculation just going off of symptoms and a small amount of information so I have to throw some other options and possible causes. I don't like the shotgun replace parts method on TBI trucks simply because of the general low quality parts that are out there. Every time I see someone shotgun parts they end bolting on a new set of problems.
As far as checking out the distributor the magnet is part of and just under the star shaped piece that spins with the shaft under the rotor. You can't see much of it, only around the shaft and in between the points of the star. If there are any cracks or pieces missing than it's junk.
One last thing, did you remove the EGR valve and physicly check to make sure there isn't any carbon stuck in the pintle or the pintle isn't hanging open? Remember new parts are only sometimes good parts.
This is purely speculation just going off of symptoms and a small amount of information so I have to throw some other options and possible causes. I don't like the shotgun replace parts method on TBI trucks simply because of the general low quality parts that are out there. Every time I see someone shotgun parts they end bolting on a new set of problems.
As far as checking out the distributor the magnet is part of and just under the star shaped piece that spins with the shaft under the rotor. You can't see much of it, only around the shaft and in between the points of the star. If there are any cracks or pieces missing than it's junk.
One last thing, did you remove the EGR valve and physicly check to make sure there isn't any carbon stuck in the pintle or the pintle isn't hanging open? Remember new parts are only sometimes good parts.
y5mgisi
1 ton status
oh ya i forgot to answer the header question, Im running stock manifolds with stock y-pipe, a cat and a flowmaster 50. what your saying does make sence though. Also just another bit of possibly helpful info is that the truck basicly just sat for about 6 months. Before i parked it it ran good/normal(it just had 213k miles on it and smoked) but then i would start it up once a month or so. And i could swear that it was sortof running like it is now. I cant say for sure cause all i ever did was start it up, let it run for a couple minutes and shut it back off. But i destinctly remember starting it one time and thinking"man this thing seems like it might need an o2 sensor" casue it wasnt running quite right.
y5mgisi
1 ton status
btw here is some numbers that i got off the scanner a couple weeks ago...
promID: 4551
IAC:39steps
temp:165.2
open loop
TPS: .62 volts
Intergrater: 128
O2:448mVolts
Knock: 0
Block learn: 126
o2 cross count:174 and rising quickly.
That scanner was not from autozone. I think im going to run up to autozone and see if thers is diffrent and will give me map values.
promID: 4551
IAC:39steps
temp:165.2
open loop
TPS: .62 volts
Intergrater: 128
O2:448mVolts
Knock: 0
Block learn: 126
o2 cross count:174 and rising quickly.
That scanner was not from autozone. I think im going to run up to autozone and see if thers is diffrent and will give me map values.
y5mgisi
1 ton status
In response to dyeager's post...
As well, here is what GM has to say about this problem in regards to possible causes:
Ignition timing Set at 4*
P/N switch circuit i dont think that could cause my particular problems
Leaking injector(s) just had them rebuilt and have the same symptoms
IAC very possible
Sticking or binding throttle shaft (incorrect TPS voltage) Seams to be fine
Vacuum leaks still possible not likely to have any but possible non the less
EGR on its new but that dosnt mean much
Bad battery cables or ground straps (erratic voltage) i inspected them when i did the motor and everything seams pretty good.
AC request dont really think so because it runns the same with the a/c compressor pluged in or left unplugged.
MAP sensor Replaved with a new one, no diffrence
AC pressure too high (not sure if that applies to trucks) actually mines pretty much empty
PCV valve bad again its new but dosnt mean its good
Compressionhavnt checked it but its a new motor and runs bad at idle only after a while, not at all times.
O2 sensor (will result in "severe driveability problem")Its new also but im Still not really sure about the 02
As well, here is what GM has to say about this problem in regards to possible causes:
Ignition timing Set at 4*
P/N switch circuit i dont think that could cause my particular problems
Leaking injector(s) just had them rebuilt and have the same symptoms
IAC very possible
Sticking or binding throttle shaft (incorrect TPS voltage) Seams to be fine
Vacuum leaks still possible not likely to have any but possible non the less
EGR on its new but that dosnt mean much
Bad battery cables or ground straps (erratic voltage) i inspected them when i did the motor and everything seams pretty good.
AC request dont really think so because it runns the same with the a/c compressor pluged in or left unplugged.
MAP sensor Replaved with a new one, no diffrence
AC pressure too high (not sure if that applies to trucks) actually mines pretty much empty
PCV valve bad again its new but dosnt mean its good
Compressionhavnt checked it but its a new motor and runs bad at idle only after a while, not at all times.
O2 sensor (will result in "severe driveability problem")Its new also but im Still not really sure about the 02
Can you get it to do these problems with the scanner attached?
Probably not, since hooking the scanner up throws off the idle and timing, but you might, see if any of the values have changed.
EGR should be fairly easy. You can test it by pushing up on the underside of the EGR valve, and seeing if the engine stumbles/dies as you push on it. If it's going to stick, when you release it, perhaps it will. You could also disconnect the EGR solenoid connector, and plug the vacuum line from the motor to the solenoid. Drive it, see if the problems come back. If they do, it's probably not your EGR, as without vacum, theoretically it shouldn't move. MAP sensor will also indicate a vacuum leak, which an EGR is.
Does the O2 actually respond by changing voltage, and can you get it to go closed loop while it sits?
Probably not, since hooking the scanner up throws off the idle and timing, but you might, see if any of the values have changed.
EGR should be fairly easy. You can test it by pushing up on the underside of the EGR valve, and seeing if the engine stumbles/dies as you push on it. If it's going to stick, when you release it, perhaps it will. You could also disconnect the EGR solenoid connector, and plug the vacuum line from the motor to the solenoid. Drive it, see if the problems come back. If they do, it's probably not your EGR, as without vacum, theoretically it shouldn't move. MAP sensor will also indicate a vacuum leak, which an EGR is.
Does the O2 actually respond by changing voltage, and can you get it to go closed loop while it sits?
y5mgisi
1 ton status
Im going to head up to autozone in a little bit here. I'll see what i can come up with. Because no ive never actually got it to "surge" with the scanner hooked up.
How do i test the o2 sensor? just to see what its reading. I know you can do it with a multimeter but i dont remember the correct way to do it.
How do i test the o2 sensor? just to see what its reading. I know you can do it with a multimeter but i dont remember the correct way to do it.
JpEater
1/2 ton status
y5mgisi said:
southern customs k5
Newbie
at gm we would sale people a new egr an induction flush they didn't need the egr tho. the induction flush was b/g two can system. poured in a pressurized can it had its own injectors pointed into the throttle body. we'd connect a hose to the exaust from the floor and watch thick white smoke outside. after words the surge was gone.it was common a problem all the techs loved because it was easy money or time took maybe 30 min payed 2.5 hours
y5mgisi
1 ton status
hmm thats weired. Does anyone know how to test for a bad IAC? And no i never actually remever the ign. modual but i belive i just sparyed the whole thing down.
Not sure what test procedure is for IAC, but if it moves while you have the scanner hooked up and play with the throttle, you can verify it's at least moving.
O2 sensor can't be tested properly with a scanner or multimeter, but you CAN verify that it is swinging rich/lean based on the voltage. As long as it's going high and low in closed loop, it's working.
O2 sensor can't be tested properly with a scanner or multimeter, but you CAN verify that it is swinging rich/lean based on the voltage. As long as it's going high and low in closed loop, it's working.
y5mgisi
1 ton status
Ok i just got back in from working on it and duing the run around with the scanner. I think i may have found the problem which is what everyone said it was from the very begining; a vacume leak. I took another can of carb clean all around the intake/egr/and TB. The only place it did anything was at the throtle shafts. On the passenger side i could allmost get the truck to die spraying carb clean where the thorttle shaft passes through. Its just weired to me that it wouldnt really show its face untill after it sat for a while. Im going to call around for a new base and if i cant find one under 150 bucks im just going to get the holly unit i think.
BTW heres what i came up with using the scanner again...
Park at idle;
O2=500-550 mVolts
Tps will often be at .8v if i let off the pedel slowly
knock was 0 the whole time
most of the time at idle it would be openloop/lean
02 drops to 190mVolts under a moderate accel.
*while surging* now just came to a stop
Iac started at 55 and slowly moved up to over 100 steps during the surging episode
gave the gas a quick tap, it setled back down, the IAC went to 29 steps and stayed there and didnt surge again
After that(still stoped but in gear idleing) it would switch breifly from lean to rich but 98% of the time it was lean.
Started driving again*
closed loop now CT at 195*
stoped again* got a surge
o2 bounced back and forth from 620 to 750 m-volts the wole time surging.
Thats it.
BTW heres what i came up with using the scanner again...
Park at idle;
O2=500-550 mVolts
Tps will often be at .8v if i let off the pedel slowly
knock was 0 the whole time
most of the time at idle it would be openloop/lean
02 drops to 190mVolts under a moderate accel.
*while surging* now just came to a stop
Iac started at 55 and slowly moved up to over 100 steps during the surging episode
gave the gas a quick tap, it setled back down, the IAC went to 29 steps and stayed there and didnt surge again
After that(still stoped but in gear idleing) it would switch breifly from lean to rich but 98% of the time it was lean.
Started driving again*
closed loop now CT at 195*
stoped again* got a surge
o2 bounced back and forth from 620 to 750 m-volts the wole time surging.
Thats it.
enginenine
Registered Member
Sounds like you found it.
I forgotten about the throttle shafts. Does the Holley unit flow better than stock?
I forgotten about the throttle shafts. Does the Holley unit flow better than stock?
Yeah, worn throttle shafts will affect TPS voltage, because the throttle shaft actually slides around in there, which means as it comes to a "close" the throttle opening the TPS is measuring is now different, at least as far as it and the ECM are concerned.
Tapping the gas and solving the problem is further evidence that the problem is likely interrelated and once you solve the throttle slop issue, both will go away. If it's bad enough to cause the problems you are haivng, you might be able to move the throttle shaft by hand vertically and notice the movement. There should be none. Might be some in/out movement to it, which is fine, but vertically or horiztontally there should be none.
Tapping the gas and solving the problem is further evidence that the problem is likely interrelated and once you solve the throttle slop issue, both will go away. If it's bad enough to cause the problems you are haivng, you might be able to move the throttle shaft by hand vertically and notice the movement. There should be none. Might be some in/out movement to it, which is fine, but vertically or horiztontally there should be none.
y5mgisi
1 ton status
I guess so. I actually found a guy here in town that said he can rebuild the base for $75. So i'll probably just do that for now. Thanks alot to everyone who helped me out so far! I really appricate it!
JpEater
1/2 ton status
southern customs k5 said:
Thats why I will NEVER take a truck to the dealer aka. stealer!
y5mgisi
1 ton status
So today i bit the bullet and had my TB base rebuilt, and put another new 02 sensor it and it still does not run correctly. As allways while driving, it runs fine. But come to a stop and in about 30 seconds, it starts stumbling and acts like it wants to die then comes back to normal then tries to die again over and over untill i tap the gas. After i tap the gas it will run good again for another 30 seconds and stat the cycle all over again. I would say that from peak to peak(allmost dieing then back up) is about 3 seconds. I hooked up a vacume guage and i have great vacume. But as it starts going into its surge(in park not in gear right now) mode it creeps into the red(late timing area) and it pulls it self out of it and the vac goes back up to normal, then it repetes that cycle over and over again. I dont know what else to do from this point.
Canadianbuilder
Registered Member
Someone may have mentioned this already but maybe your distributor is the probem?worn shaft or bushings?.Possibly some other defect with the pickups or possibly a bad coil?Just offering some more suggestions.I`d like to know what the problem is when you get it solved.Good luck.
K5Greek
1/2 ton status
dude im telling you ive been there with the surge and my problem was the ignition module.. mine wouldnt act up while cold but once she got warm it would start surging.. and same thing if i tapped the gas it would run right for a few second then repeat process..
ive replaced everything egr, o2, plug, wire, rotor, checked for vacumn leaks many times and nothing happened..
and when it finally goes bad you wont be able to give the truck any throttle or itll start back firing
ive replaced everything egr, o2, plug, wire, rotor, checked for vacumn leaks many times and nothing happened..
and when it finally goes bad you wont be able to give the truck any throttle or itll start back firing
Not to keep harping on the Dizzy, but I know that if your pick-up coil (That tone ring on the shaft) has a crack, or isn't quite aligned right, you can have rough idle problems.
That ring is the very foundation of your engine timing. It is what tells the dizzy/computer how fast the engine is spinning and where the cam is in its cycle. If there is anything wrong there, it could lead to all sorts of problems.
(The fact that you had to dial in 4 degrees to get it to run makes me suspect this even more)
Also: Your ignition module NEEDS that grease between it and the distributor. That is a heat conducting grease (special) and it allows the module to stay cool by transferring the heat to the body of the distributor. If you that grease was compromised, pull the module and put fresh grease in there. (I THINK you can even get your module 'checked' while you have it out to make sure it is not damaged).
Good luck man. Just don't overlook the dizzy in your search for the answer!
That ring is the very foundation of your engine timing. It is what tells the dizzy/computer how fast the engine is spinning and where the cam is in its cycle. If there is anything wrong there, it could lead to all sorts of problems.
(The fact that you had to dial in 4 degrees to get it to run makes me suspect this even more)
Also: Your ignition module NEEDS that grease between it and the distributor. That is a heat conducting grease (special) and it allows the module to stay cool by transferring the heat to the body of the distributor. If you that grease was compromised, pull the module and put fresh grease in there. (I THINK you can even get your module 'checked' while you have it out to make sure it is not damaged).
Good luck man. Just don't overlook the dizzy in your search for the answer!
