RPMs fluctuate
Thread Starter
Junior Member
Joined: Aug 2013
Posts: 29
Likes: 0
From: Wisconsin
Car: 1986 Camaro
Engine: 305 TPI
Transmission: Auto
Axle/Gears: Stock
RPMs fluctuate
This is my first post. My 86 IROC-Z Z28 (just to confirm it is the TPI 305 with an auto trans) is idling sporadically. It is not consistent, it happens when i first start it, after it has been idling for a while, while im driving. When i first start it too it starts fine but then it either idles low or dies right away, if i try to step on the gas just a little it will lose power and often die if it is idling low when i try to get going. The car shows code 33 which i know is the MAF or ECM or a short in the wiring, I had the ECM replaced 2 years ago and the car had the same problems before then. I replaced the MAF, that helped. I replaced the catalytic converter because the catalyst was busted up and plugging the exhaust. That helped too but the problem is still not fixed. I have also replaced my Idle Air Control Valve, PCV, O2 sensor, fuel filter, TPS, ignition wires, spark plugs, and air filters. I'm running out of options especially what im capable of at home. I have the Haynes repair manual so my trouble shooting source should be legit. The book also says that the loping while idling can be caused by vacuum leaks in the EGR or tubes, also mentions timing problems and worn camshaft lobes. I'm not sure what to attack next on it. I don't exactly have a ton of money to put into the car, it has been bleeding me all summer. What can all of you say from your experience with these cars?
Thread Starter
Junior Member
Joined: Aug 2013
Posts: 29
Likes: 0
From: Wisconsin
Car: 1986 Camaro
Engine: 305 TPI
Transmission: Auto
Axle/Gears: Stock
Re: RPMs fluctuate
Also I am no professional. I am figuring all this out as I go. So any diagrams or links to guides would be helpful. For example if it is all the vacuum hoses i would not know what and where they all are. I haven't been able to find in my repair manual if it shows all that. Thank you and I appreciate any help.
Joined: Dec 2012
Posts: 407
Likes: 10
From: Clarksville,TN
Car: 1989 GTA
Engine: 5.7 w/Paxton
Transmission: 700R4
Axle/Gears: 3.27
Re: RPMs fluctuate
Did you go through the flow chart for a code 33? Probably a good place to start. Then a vacuum test. Definitely check the intake boots to make sure all is tight.
Here is the flow chart....
Unplug the MAF and take a voltage reading of the drk green wire with the key in the run position and the engine off.
Have you recently changed the MAF power or burn-off relays?
My code 33 is pointing to the ECM, but you need to do these things first as this 33 is a very popular code for OBD1 TPI cars.
Here is the flow chart....
Unplug the MAF and take a voltage reading of the drk green wire with the key in the run position and the engine off.
Have you recently changed the MAF power or burn-off relays?
My code 33 is pointing to the ECM, but you need to do these things first as this 33 is a very popular code for OBD1 TPI cars.
Last edited by MrPackstin; Aug 19, 2013 at 01:15 AM.
Thread Starter
Junior Member
Joined: Aug 2013
Posts: 29
Likes: 0
From: Wisconsin
Car: 1986 Camaro
Engine: 305 TPI
Transmission: Auto
Axle/Gears: Stock
Re: RPMs fluctuate
No I haven't tried those yet the check engine light is also not constantly on it usually flashes when the RPMs fluctuate.
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From: Chasing Electrons
Car: check
Engine: check
Transmission: check
Re: RPMs fluctuate
RBob.
Thread Starter
Junior Member
Joined: Aug 2013
Posts: 29
Likes: 0
From: Wisconsin
Car: 1986 Camaro
Engine: 305 TPI
Transmission: Auto
Axle/Gears: Stock
Re: RPMs fluctuate
I don't think it would be the ECM. I had it replaced a couple years ago. Ill try what Mr Packstin said and use the flow chart but i dont know how much of it i can do myself.
Member
Joined: Aug 2013
Posts: 113
Likes: 1
Re: RPMs fluctuate
Vacuum leak test FIRST.
[quote=Schrade;5616145]
Order of operations.
Vacuum leak.
Do this. PERFECTLY.
(Most mechanics can't do it well, and / or don't know how)
[quote]
and we're sure lucky to have some others on the boards uH-Huh yUp
[quote=Schrade;5616145]
Order of operations.
Vacuum leak.
Do this. PERFECTLY.
Originally Posted by Schrade
Vacuum leak detection is hard to do right: I know of only one guy who did it right and found a leak (in IAC gasket):
Quote:
Originally Posted by Schrade View Post
No one got the proper technique for vacuum leak detection...
FIRST (fully warmed up motor); block the gas pedal, or block the throttle linkage. YOU HAVE TO DO THIS TO GET A STEADY IDLE , around 1,250 rpms, or a little higher. If you don't, you can fish starting fluid, a propane hose, or WD40, or Krylon, or hair spray, or pee, anything, until you need a sweater in Hades, but if the motor is lopin' idle already from a vacuum leak, you ain't gonna' find any leak, unless it's so big that Little Jack Horner can stick his thumb in it and pull out a pineapple NOPE.
AFTER you get a steady idle, THEN, you can spray starting fluid everywhere - that's the best detector, because it's vapor pressure is very high - a LITTLE at a time, all around the motor, until you get the rpm SURGE. Follow the vacuum lines to the EVAP cannister too. You might even have to follow the EVAP lines from the EVAP cannister to the gas tank too, but that vacuum leak will show up as a DTC 32 EGR fault, and won't normally show as loping idle, unless the EVAP cannister has been by-passed (been there, saw that uh-HUH yup).
If you get a surge in a tight spot, and can't tell exactly where it is, light a book of matches, blow out the match heads while they're still burnin', and feed the smoke to the tight spot to see it get drawn in.
Fear not the starting fluid; you cannot put the can down fast enough and light the matches fast enough to catch the starting fluid, because the vapor pressure is so high.
Bookmark this post YUP.
Wrench Wizard OUT!
Vacuum leak detection is hard to do right: I know of only one guy who did it right and found a leak (in IAC gasket):
Quote:
Originally Posted by Schrade View Post
No one got the proper technique for vacuum leak detection...
FIRST (fully warmed up motor); block the gas pedal, or block the throttle linkage. YOU HAVE TO DO THIS TO GET A STEADY IDLE , around 1,250 rpms, or a little higher. If you don't, you can fish starting fluid, a propane hose, or WD40, or Krylon, or hair spray, or pee, anything, until you need a sweater in Hades, but if the motor is lopin' idle already from a vacuum leak, you ain't gonna' find any leak, unless it's so big that Little Jack Horner can stick his thumb in it and pull out a pineapple NOPE.
AFTER you get a steady idle, THEN, you can spray starting fluid everywhere - that's the best detector, because it's vapor pressure is very high - a LITTLE at a time, all around the motor, until you get the rpm SURGE. Follow the vacuum lines to the EVAP cannister too. You might even have to follow the EVAP lines from the EVAP cannister to the gas tank too, but that vacuum leak will show up as a DTC 32 EGR fault, and won't normally show as loping idle, unless the EVAP cannister has been by-passed (been there, saw that uh-HUH yup).
If you get a surge in a tight spot, and can't tell exactly where it is, light a book of matches, blow out the match heads while they're still burnin', and feed the smoke to the tight spot to see it get drawn in.
Fear not the starting fluid; you cannot put the can down fast enough and light the matches fast enough to catch the starting fluid, because the vapor pressure is so high.
Bookmark this post YUP.
Wrench Wizard OUT!
[quote]
and we're sure lucky to have some others on the boards uH-Huh yUp
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Thread Starter
Junior Member
Joined: Aug 2013
Posts: 29
Likes: 0
From: Wisconsin
Car: 1986 Camaro
Engine: 305 TPI
Transmission: Auto
Axle/Gears: Stock
Re: RPMs fluctuate
Thanks guys I replaced my MAF Burn off relay that seemed to do the trick. Had to do some digging at Carquest to get a part number.
Supreme Member
Joined: Jun 2011
Posts: 2,036
Likes: 5
From: knoxville tn
Car: 86 IROC
Engine: 5.0 TPI
Transmission: 700-R-4
Axle/Gears: 2.73 open
Re: RPMs fluctuate
This is my first post. My 86 IROC-Z Z28 (just to confirm it is the TPI 305 with an auto trans) is idling sporadically. It is not consistent, it happens when i first start it, after it has been idling for a while, while im driving. When i first start it too it starts fine but then it either idles low or dies right away, if i try to step on the gas just a little it will lose power and often die if it is idling low when i try to get going. The car shows code 33 which i know is the MAF or ECM or a short in the wiring, I had the ECM replaced 2 years ago and the car had the same problems before then. I replaced the MAF, that helped. I replaced the catalytic converter because the catalyst was busted up and plugging the exhaust. That helped too but the problem is still not fixed. I have also replaced my Idle Air Control Valve, PCV, O2 sensor, fuel filter, TPS, ignition wires, spark plugs, and air filters. I'm running out of options especially what im capable of at home. I have the Haynes repair manual so my trouble shooting source should be legit. The book also says that the loping while idling can be caused by vacuum leaks in the EGR or tubes, also mentions timing problems and worn camshaft lobes. I'm not sure what to attack next on it. I don't exactly have a ton of money to put into the car, it has been bleeding me all summer. What can all of you say from your experience with these cars?
Thread Starter
Junior Member
Joined: Aug 2013
Posts: 29
Likes: 0
From: Wisconsin
Car: 1986 Camaro
Engine: 305 TPI
Transmission: Auto
Axle/Gears: Stock
Re: RPMs fluctuate
The manual has been helpful thus far. It may not be perfect but its better than nothing. I really do appreciate the advice guys!
Also my car has been running better but it still dies often when the car is idling. Especially when i first start it. It idles low most of the time and if i step on the gas the rpm's just go down and the car shuts off. This happens no matter how hard i step on the gas very lightly, or very hard. The car lacks power when i drive, but it doesnt die when the rpms are high. It backfires sometimes when idling down from a higher rpm. What could this be timing, or misfire? I just wanted some idea of what it might be so i don't have to spend a bunch of money on something it likely is not.
Also my car has been running better but it still dies often when the car is idling. Especially when i first start it. It idles low most of the time and if i step on the gas the rpm's just go down and the car shuts off. This happens no matter how hard i step on the gas very lightly, or very hard. The car lacks power when i drive, but it doesnt die when the rpms are high. It backfires sometimes when idling down from a higher rpm. What could this be timing, or misfire? I just wanted some idea of what it might be so i don't have to spend a bunch of money on something it likely is not.
Supreme Member
Joined: Jun 2011
Posts: 2,036
Likes: 5
From: knoxville tn
Car: 86 IROC
Engine: 5.0 TPI
Transmission: 700-R-4
Axle/Gears: 2.73 open
Re: RPMs fluctuate
The manual has been helpful thus far. It may not be perfect but its better than nothing. I really do appreciate the advice guys!
Also my car has been running better but it still dies often when the car is idling. Especially when i first start it. It idles low most of the time and if i step on the gas the rpm's just go down and the car shuts off. This happens no matter how hard i step on the gas very lightly, or very hard. The car lacks power when i drive, but it doesnt die when the rpms are high. It backfires sometimes when idling down from a higher rpm. What could this be timing, or misfire? I just wanted some idea of what it might be so i don't have to spend a bunch of money on something it likely is not.
Also my car has been running better but it still dies often when the car is idling. Especially when i first start it. It idles low most of the time and if i step on the gas the rpm's just go down and the car shuts off. This happens no matter how hard i step on the gas very lightly, or very hard. The car lacks power when i drive, but it doesnt die when the rpms are high. It backfires sometimes when idling down from a higher rpm. What could this be timing, or misfire? I just wanted some idea of what it might be so i don't have to spend a bunch of money on something it likely is not.
Thread Starter
Junior Member
Joined: Aug 2013
Posts: 29
Likes: 0
From: Wisconsin
Car: 1986 Camaro
Engine: 305 TPI
Transmission: Auto
Axle/Gears: Stock
Re: RPMs fluctuate
The car will still fluctuate a little sometimes, but it is far less often. I may also try replacing the cap and rotor.
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