Intermittent Idle / Timing problem
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Joined: Nov 2002
Posts: 77
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From: Chicago Suburbs
Re: Intermittent Idle / Timing problem (ittlfly)
As for popping and missing first thing I would do is put a simple vacuume guage on the car to see if it could be an intake valve. If the vacuume guage is bouncing all over the place I would suspect a cracked, bent or damaged valve seat on an intake valve. The other thing I would check is of all things the tiny drain hole in the back gas tank filler grommet. Believe it or not if it rains alot and the car has a plugged up hole it will suck in water in the gas. The water in the gas will seperate from the gas and go to the bottom of the tank over night. Then when you drive it will shake up with the gas and the car will start running better with a pop or a miss every once in a while along with pinging (simply fix this by dumping two or three bottles of HEET gas antifreez or isopropal alcohol). This is an example of how different the same problem can be and I sure wish I could come out to sunny C.A. but it IS deicing season and I am stuck where I am needed by my Illustrious Airline Career...LOL
Some other things to look at are timing chain slop (get the motor where you can see the water pump drive shaft (LT1) or distributer (L98) and rotate the motor until the pump/distributer move. Mark the front balancer and something stationary and rotate the motor the opposite way until you see the pump/distributer move again. This is the slop in your chain and anything over 8 degrees or so will effect the motor. A simple removal of the valve covers will let you know if cam lobes are worn down. And by all means everybody check the obvious plug wires on wrong. An LT1 will run pretty good even if plug wires are crossed. Compression tests are free but take a lot of time and they never lie. I have seen cylinders blown between yet no oil or antifreeze problems.
I would ask myself first and foremost does the problem ever go away or is it there always. I would drive the car alot and try to feel if the problem seems to go away or is the fuel injection trying to cover it up. Even though injection is wonderful for the state of tune cars are in today, injection can also make it a lot harder to troubleshoot because the computer can kill individual injectors so fuel can be shut off on a hole that has a misfire. The condition of the spark plugs is a sure bet of a misfire. If you suspect plug wires and get symptoms only in wet or rainy days, use windex window cleaner on a dark night or in a dark room and spray down those wires and anything else you want to see if there is blue spark leaking out. The windex will dry quickly on a hot motor and not leave you stranded later. If you want to try and draw out the spark just hook your test light to ground and move the point around the wires to see if spark tries to jump out (the test light will keep you from feeling a part of your car that you never want to feel...lol). DO NOT DO THIS ON Distributerless Ignitons!!!! These are FREE and easy tests for the most part that will not break your bank only your time. If anyone wants to get real specific with their problem, give me great detail of what driving your car is like from the time you get in it cold to the time it is completely hot and I will try and help some more but I don't want to suggest replacing parts to anyone unless I am absolute sure of the problem. To get absolutely sure for me is almost impossible but I am willing to give it a try. I have seen so many strange things end up being the problem on cars and I have developed an attitude that when I diagnose a car I think about what is happening and what is the most obvious thing it could be. I have seen people do tune ups and accidently drop a plug or not check plug gap and a plug which has a gap that is ALMOST closed WILL cause all sorts of problems with a motor. The other thing you need to think about is what wears the most. Obviously the throttle body is always moving with your foot so the plates and TPS move constantly and the TPS is just a pot like a stereo **** and can go bad like a stereo **** volume controll. To check the TPS, hook a digital volt meter to the wire leads (with TPS unplugged), (forget the colors but it is the center wire and one of the outside ones) and open up the TPS slowly while checking the resistance. You should see the resistance gradually change WITHOUT SKIPPING numbers. If you see the resistance jump past some numbers, try to go back to the missed numbers and if you can't get them chances are you have a bad TPS. Most mechanics carry a spare test TPS to save time with this test but it is free so go for it. You can test the tps LIVE with voltage the same way on GM's by sliding paper clips in and with the ignition on, take a look at the voltage sweep and see if there are skips. The MAP sensor has a vaccume port and with the paper clip thing can be checked similar to the TPS but you need a vaccume pump to apply and slowly release the vaccume while watching voltage to make sure the MAP is ok. The IAC can be its own bear because it may be working to the computer but the gears could be worn out and the computer would never see it. All the computer would know is it is trying to make a change with the IAC and the IAC is taking the command with no shorts while the gear may not be cooperating. On other things that may need testing give me a question and I will (or even others) try my best to give the proper test procedure.... :thumbs:
Some other things to look at are timing chain slop (get the motor where you can see the water pump drive shaft (LT1) or distributer (L98) and rotate the motor until the pump/distributer move. Mark the front balancer and something stationary and rotate the motor the opposite way until you see the pump/distributer move again. This is the slop in your chain and anything over 8 degrees or so will effect the motor. A simple removal of the valve covers will let you know if cam lobes are worn down. And by all means everybody check the obvious plug wires on wrong. An LT1 will run pretty good even if plug wires are crossed. Compression tests are free but take a lot of time and they never lie. I have seen cylinders blown between yet no oil or antifreeze problems.
I would ask myself first and foremost does the problem ever go away or is it there always. I would drive the car alot and try to feel if the problem seems to go away or is the fuel injection trying to cover it up. Even though injection is wonderful for the state of tune cars are in today, injection can also make it a lot harder to troubleshoot because the computer can kill individual injectors so fuel can be shut off on a hole that has a misfire. The condition of the spark plugs is a sure bet of a misfire. If you suspect plug wires and get symptoms only in wet or rainy days, use windex window cleaner on a dark night or in a dark room and spray down those wires and anything else you want to see if there is blue spark leaking out. The windex will dry quickly on a hot motor and not leave you stranded later. If you want to try and draw out the spark just hook your test light to ground and move the point around the wires to see if spark tries to jump out (the test light will keep you from feeling a part of your car that you never want to feel...lol). DO NOT DO THIS ON Distributerless Ignitons!!!! These are FREE and easy tests for the most part that will not break your bank only your time. If anyone wants to get real specific with their problem, give me great detail of what driving your car is like from the time you get in it cold to the time it is completely hot and I will try and help some more but I don't want to suggest replacing parts to anyone unless I am absolute sure of the problem. To get absolutely sure for me is almost impossible but I am willing to give it a try. I have seen so many strange things end up being the problem on cars and I have developed an attitude that when I diagnose a car I think about what is happening and what is the most obvious thing it could be. I have seen people do tune ups and accidently drop a plug or not check plug gap and a plug which has a gap that is ALMOST closed WILL cause all sorts of problems with a motor. The other thing you need to think about is what wears the most. Obviously the throttle body is always moving with your foot so the plates and TPS move constantly and the TPS is just a pot like a stereo **** and can go bad like a stereo **** volume controll. To check the TPS, hook a digital volt meter to the wire leads (with TPS unplugged), (forget the colors but it is the center wire and one of the outside ones) and open up the TPS slowly while checking the resistance. You should see the resistance gradually change WITHOUT SKIPPING numbers. If you see the resistance jump past some numbers, try to go back to the missed numbers and if you can't get them chances are you have a bad TPS. Most mechanics carry a spare test TPS to save time with this test but it is free so go for it. You can test the tps LIVE with voltage the same way on GM's by sliding paper clips in and with the ignition on, take a look at the voltage sweep and see if there are skips. The MAP sensor has a vaccume port and with the paper clip thing can be checked similar to the TPS but you need a vaccume pump to apply and slowly release the vaccume while watching voltage to make sure the MAP is ok. The IAC can be its own bear because it may be working to the computer but the gears could be worn out and the computer would never see it. All the computer would know is it is trying to make a change with the IAC and the IAC is taking the command with no shorts while the gear may not be cooperating. On other things that may need testing give me a question and I will (or even others) try my best to give the proper test procedure.... :thumbs:
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Joined: Nov 2002
Posts: 77
Likes: 0
From: Chicago Suburbs
Re: Intermittent Idle / Timing problem (lani's 93)
That's great you found the problem lani. I am curious now, some GM's build up a current or electrical charge in the coolant system. If you read this and have a chance, see if you have any millivolts if you put the lead of a DVOM (Volt Meter) in the water side of the radiator cap and the other to the brass or aluminum radiator cap surround or ground on the motor. If you see a charge or the water looks "rusty" in color, flush your baby but don't get any water on that opti.... :thumbs:
