Idle speed too high
Idle speed too high
Hi everyone
As winter's coming in here in Switzerland and it's not too funny driving like this in snow, I wanted to take care of my high idle speed.
I've had the problem for at least one and half a year now. Normally idle was around 1500rpms when cold and then soon came down to ~700-750 rpms. But then, quite unnoticed - so not suddenly - I felt that the engine keeps pulling when I'm on the brakes and also in neutral position that the idle didn't really go under 1500rpms anymore, it even was over 2000rpms quite often. I also linked this problem to my higher fuel consumption which I slowly noticed. Before, I did about 380 kilometers with a full tank, now it's 320 maximum but was surely - at least partly - due to another route to work (over a hill). The high idle problem remains, though.
First my question to you... what could be the cause for a higher fuel consumption and, above all, the high idle? I thought of 5 things: very old spark plugs and wires (bad ignition), defective or a CTS (or any other sensor) intermittently giving wrong values, a defective IAC-valve, defective TPS or a vacuum leakage. What do you think?
I'd just have bought a new IAC-valve and TPS to change them cleaning the inside of the TBI if necessary while I'm at it. But maybe you have some better approach.
Yesterday, I measured the CTS-values as sometime ago I thought the fan didn't come on at the specified temperature but only at the second temperature level. Now I measured as follows:
5500 Ohms in cold condition (engine not running). At about 153 Ohms the fan kicked in (at about 163 went out again), reproducible. After stopping the engine the temperature rose to 140 Ohms and coolant was pressed out of my reservoir while the water was boiling (which has been another problem for more than 5 years).
Am I right that the measured values are okay and so the sensor and both the cable to the ECM and the ECM should be alright? I was a bit irritated. I had the table about temperature-to-resistance out of this forum next to me. There it says 75 Ohms are 115° Celsius, in the GM manual it says that 70 Ohms are about 130° Celsius. Later on the diagnostic pages there is a table which only goes up to 100° Celsius but the values there correspond to the Thirdgen table again...?? But actually the 153 Ohms should be at least somwhere around 110° Celsius (+/- 5 degrees) and therefore where the fan has to kick in.
What else could I test to find the reason for my problem?
Thanks,
Thomas
As winter's coming in here in Switzerland and it's not too funny driving like this in snow, I wanted to take care of my high idle speed.
I've had the problem for at least one and half a year now. Normally idle was around 1500rpms when cold and then soon came down to ~700-750 rpms. But then, quite unnoticed - so not suddenly - I felt that the engine keeps pulling when I'm on the brakes and also in neutral position that the idle didn't really go under 1500rpms anymore, it even was over 2000rpms quite often. I also linked this problem to my higher fuel consumption which I slowly noticed. Before, I did about 380 kilometers with a full tank, now it's 320 maximum but was surely - at least partly - due to another route to work (over a hill). The high idle problem remains, though.
First my question to you... what could be the cause for a higher fuel consumption and, above all, the high idle? I thought of 5 things: very old spark plugs and wires (bad ignition), defective or a CTS (or any other sensor) intermittently giving wrong values, a defective IAC-valve, defective TPS or a vacuum leakage. What do you think?
I'd just have bought a new IAC-valve and TPS to change them cleaning the inside of the TBI if necessary while I'm at it. But maybe you have some better approach.
Yesterday, I measured the CTS-values as sometime ago I thought the fan didn't come on at the specified temperature but only at the second temperature level. Now I measured as follows:
5500 Ohms in cold condition (engine not running). At about 153 Ohms the fan kicked in (at about 163 went out again), reproducible. After stopping the engine the temperature rose to 140 Ohms and coolant was pressed out of my reservoir while the water was boiling (which has been another problem for more than 5 years).
Am I right that the measured values are okay and so the sensor and both the cable to the ECM and the ECM should be alright? I was a bit irritated. I had the table about temperature-to-resistance out of this forum next to me. There it says 75 Ohms are 115° Celsius, in the GM manual it says that 70 Ohms are about 130° Celsius. Later on the diagnostic pages there is a table which only goes up to 100° Celsius but the values there correspond to the Thirdgen table again...?? But actually the 153 Ohms should be at least somwhere around 110° Celsius (+/- 5 degrees) and therefore where the fan has to kick in.
What else could I test to find the reason for my problem?
Thanks,
Thomas