Confused with weird symptoms
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Joined: Dec 2023
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From: IA
Confused with weird symptoms
Hello, everyone. I have a 2002 Saturn SL1 with high rev at start-up and general higher idle (around 1.1k to 900rpm) when warm (quarter mark on temp gauge). I have very bad gas mileage. I used to get almost 300 miles on a tank, now about 176 miles. When the idle is bad, it revs to 1.5k rpm every down shift and will coast with little slow down if you know what I mean. I've replaced the Tps now for the second time with an NGK, cleaned TB and IAC sensor. I have replaced MAP sensor, it charges At 14.2v, no vacuum leak, replaced intake manifold gasket and ECT sensor (no visible corrosion on pigtail). Still have no idea what is causing the issue and would like to fix soon. I also see the low coolant light on every once and a while when it is cold outside but coolant level seems to be pretty good.
Do you guys have any ideas? I hope its not a PCM.
Do you guys have any ideas? I hope its not a PCM.
Super Moderator
Joined: Jul 2005
Posts: 12,315
From: Slightly off center
1) Any codes?
2) What plugs are you using?
3) How many miles on plugs?
4) How many miles on front O2 sensor. And what brand?
How many miles on the engine?
2) What plugs are you using?
3) How many miles on plugs?
4) How many miles on front O2 sensor. And what brand?
How many miles on the engine?
Last edited by derf; Dec 29, 2023 at 02:05 AM.
Super Moderator
Joined: Jul 2005
Posts: 12,315
From: Slightly off center
1500 rpm on every downshift? Do you mean when you put the clutch all the way in? But not always?
When did this start?
What brand TPS?
Did you scrape the block and manifold mating surfaces completely clean before installing the replacement?
Most of the questions I've posed center around things that would cause your engine to consume more fuel per unit time than it should.
Front O2 sensor and ECTS have the most influence on the air fuel mix. If your front O2 sensor is poisoned / worn out it usually will not detect as much oxygen as they're actually is in the exhaust. It thinks the engine is running lean so it riches the fuel Air Max. Also known as uses more gas.
If ECTS is reading abnormally low, PCM richins the mixture because it thinks the answer is at a lower temperature than it is. Also known as uses more gas.
If there is a vacuum link, there is air getting into one or more of the cylinders that has not been accounted for in calculating the fuel/air mix based on the O2 sensor reading. In this situation, that air leans out the overall mixture, there is less oxygen detected at the O2 sensor and the PCM richens the mixture until it sees the expected amount of oxygen in the exhaust. Also known as using more gas.
If your plugs are worn out/gaps too wide, you will get inefficient combustion from a weak Spark. Also known as using more gas.
If they are the wrong plugs, you may also get crap mileage from the get-go. Also known as using more gas.
If the TPS an actual throttle position are not in sync, you may get these strange idle problems. When it is revving at 1500, safely pull off the road and turn the engine off. Remove the key. Wait 10 seconds, restart the vehicle. If the 1500 RPM disappears, it usually points to the TPS. So my next question is what brand of TPS are you using? Most electronic aftermarket parts are crap for these cars. Not all, but most.
Honestly I think you have more than one problem going on. Did you spray the intake manifold very very very thoroughly including from the underside with throttle body cleaner after you did the replacement? It is very easy to miss leaks that you cannot access from the top.
Also, did you follow the torque specs and tightening order? The torque spec is quite low and the tightening sequence is to ensure you minimize stress on the intake manifold that might otherwise make it slightly less than a flat when mating, causing a vac leak.
I would read the OBD2 measurements to ensure the ECTS is reading correctly and that the front O2 is behaving normally. I doubt it is.
When did this start?
What brand TPS?
Did you scrape the block and manifold mating surfaces completely clean before installing the replacement?
Most of the questions I've posed center around things that would cause your engine to consume more fuel per unit time than it should.
Front O2 sensor and ECTS have the most influence on the air fuel mix. If your front O2 sensor is poisoned / worn out it usually will not detect as much oxygen as they're actually is in the exhaust. It thinks the engine is running lean so it riches the fuel Air Max. Also known as uses more gas.
If ECTS is reading abnormally low, PCM richins the mixture because it thinks the answer is at a lower temperature than it is. Also known as uses more gas.
If there is a vacuum link, there is air getting into one or more of the cylinders that has not been accounted for in calculating the fuel/air mix based on the O2 sensor reading. In this situation, that air leans out the overall mixture, there is less oxygen detected at the O2 sensor and the PCM richens the mixture until it sees the expected amount of oxygen in the exhaust. Also known as using more gas.
If your plugs are worn out/gaps too wide, you will get inefficient combustion from a weak Spark. Also known as using more gas.
If they are the wrong plugs, you may also get crap mileage from the get-go. Also known as using more gas.
If the TPS an actual throttle position are not in sync, you may get these strange idle problems. When it is revving at 1500, safely pull off the road and turn the engine off. Remove the key. Wait 10 seconds, restart the vehicle. If the 1500 RPM disappears, it usually points to the TPS. So my next question is what brand of TPS are you using? Most electronic aftermarket parts are crap for these cars. Not all, but most.
Honestly I think you have more than one problem going on. Did you spray the intake manifold very very very thoroughly including from the underside with throttle body cleaner after you did the replacement? It is very easy to miss leaks that you cannot access from the top.
Also, did you follow the torque specs and tightening order? The torque spec is quite low and the tightening sequence is to ensure you minimize stress on the intake manifold that might otherwise make it slightly less than a flat when mating, causing a vac leak.
I would read the OBD2 measurements to ensure the ECTS is reading correctly and that the front O2 is behaving normally. I doubt it is.
Super Moderator
Joined: Jul 2005
Posts: 12,315
From: Slightly off center
I was saving that up in case he answered......
But alas, it is true.
Sometimes when I move a post to the category it should have been in in the first place, a very small percentage of people can't figure out how to find their post. Like searching for part of the title maybe? Or their username?
I could leave redirects, but then all we have is the new member section with 1700 redirects and we just ain't going there. It's really not that hard to put a vue question in the Vue section.
If you can't figure out how to find your post that was moved, well,......
But alas, it is true.
Sometimes when I move a post to the category it should have been in in the first place, a very small percentage of people can't figure out how to find their post. Like searching for part of the title maybe? Or their username?
I could leave redirects, but then all we have is the new member section with 1700 redirects and we just ain't going there. It's really not that hard to put a vue question in the Vue section.
If you can't figure out how to find your post that was moved, well,......
