Idle/major fuel usage issue
04-29-09, 09:13 AM
#1
Full Member
Thread Starter
Join Date: Aug 2005
Location: Cairns, Australia
Posts: 83
Likes: 0
Received 0 Likes
on
0 Posts
Idle/major fuel usage issue
Hi all,
Yes it's another idle problem thread. I've seen people post with this issue before but I can't find anything in the threads as per a solution.
When starting up the car:
Turn the key after waiting a few seconds for the pump to start, car starts up pretty much straight away as normal etc. jumps up to 3000rpm then drops back down to 1500, and stays there for about 45 seconds before dropping down to about 1200 and surging back up to 1400 and repeating this for about 10 seconds. It then proceeds to idle at about 1200 and it's happy.
When driving:
Uses far too much fuel for a start, I'm getting 150km to a full tank of fuel which is just insane really, exhaust smells heavily of fuel so I know I'm running rich, but the car seems to run just fine. When stopped at lights car either a) Idles at 1500 or b) Surges between 1200-1500. HOWEVER if I am to release the clutch enough that the car starts rolling, the idle steadies out to an even 1500 or just below and is rock steady.
Lights: This is a new one, when I had my lights on I realised that when I turned on my indicators my dash lights are dimming slightly, not sure if this is a battery related issue or a alt issue? Or maybe my stereo is just killing my dash lights a bit. Doesn't seem to cause it a problem.
AC: When the AC is turned on I get a dead steady 1000rpm idle. The car is also so bogged down with it on it's almost undriveable unless I launch from about 3000rpm. It feels like it's going to stall if I don't give a boot to the throttle on launch with the AC on.
I am absolutely stumped with this problem. Vacuum hoses are about to get replaced so I can find out if it is vacuum but it doesn't seem likely to be entirely vacuum as that would not explain the massive fuel usage.
Possible Culprits:
BAC - Explains crap idle and steadying idle with AC on - doesn't explain fuel usage
TPS - Explains crap idle and why slipping on the clutch steadies idle out? Doesn't explain fuel usage
Major vacuum leak - Explains idle and horrible throttle response from a launch. Doesn't explain fuel usage
Coolant Temp Switch (cold start system) - Explains major fuel usage and high idle as it could constantly be in cold start mode. However I get the same fuel usage and high idle when I start with clutch in while in gear therefore disabling cold start.
AFM - Explains major fuel usage?
FPR - Explains fuel usage and heavy exhaust smell, doesn't explain idle
Leaking injectors - See above
Fuel pump - See above (maybe clogged?)
Is anyone able to shed some light on this so I know what to organise replacement of first rather than just replacing everything? That gets expensive fast. I do have a spare AFM here as well as a couple of other things, injectors are off to get cleaned probably next week and silicone vacuum hoses will be heading in there in the next couple of weeks. Any light you can shed is much appreciated.
Thanks,
Sean
Yes it's another idle problem thread. I've seen people post with this issue before but I can't find anything in the threads as per a solution.
When starting up the car:
Turn the key after waiting a few seconds for the pump to start, car starts up pretty much straight away as normal etc. jumps up to 3000rpm then drops back down to 1500, and stays there for about 45 seconds before dropping down to about 1200 and surging back up to 1400 and repeating this for about 10 seconds. It then proceeds to idle at about 1200 and it's happy.
When driving:
Uses far too much fuel for a start, I'm getting 150km to a full tank of fuel which is just insane really, exhaust smells heavily of fuel so I know I'm running rich, but the car seems to run just fine. When stopped at lights car either a) Idles at 1500 or b) Surges between 1200-1500. HOWEVER if I am to release the clutch enough that the car starts rolling, the idle steadies out to an even 1500 or just below and is rock steady.
Lights: This is a new one, when I had my lights on I realised that when I turned on my indicators my dash lights are dimming slightly, not sure if this is a battery related issue or a alt issue? Or maybe my stereo is just killing my dash lights a bit. Doesn't seem to cause it a problem.
AC: When the AC is turned on I get a dead steady 1000rpm idle. The car is also so bogged down with it on it's almost undriveable unless I launch from about 3000rpm. It feels like it's going to stall if I don't give a boot to the throttle on launch with the AC on.
I am absolutely stumped with this problem. Vacuum hoses are about to get replaced so I can find out if it is vacuum but it doesn't seem likely to be entirely vacuum as that would not explain the massive fuel usage.
Possible Culprits:
BAC - Explains crap idle and steadying idle with AC on - doesn't explain fuel usage
TPS - Explains crap idle and why slipping on the clutch steadies idle out? Doesn't explain fuel usage
Major vacuum leak - Explains idle and horrible throttle response from a launch. Doesn't explain fuel usage
Coolant Temp Switch (cold start system) - Explains major fuel usage and high idle as it could constantly be in cold start mode. However I get the same fuel usage and high idle when I start with clutch in while in gear therefore disabling cold start.
AFM - Explains major fuel usage?
FPR - Explains fuel usage and heavy exhaust smell, doesn't explain idle
Leaking injectors - See above
Fuel pump - See above (maybe clogged?)
Is anyone able to shed some light on this so I know what to organise replacement of first rather than just replacing everything? That gets expensive fast. I do have a spare AFM here as well as a couple of other things, injectors are off to get cleaned probably next week and silicone vacuum hoses will be heading in there in the next couple of weeks. Any light you can shed is much appreciated.
Thanks,
Sean
04-29-09, 01:00 PM
#2
I'd start with changing the oxygen sensor if you are seeing a large increase in fuel consumption.
You may want to unplug it and see if it makes a difference. If it doesn't go full rich, consider a replacement.
For searching idle, try setting the throttle position sensor first.
Next check your BAC valve. With the engine running, unplug it and the clicking should stop.
For lowering the idle, check for vacuum leaks that are causing the idle to run high.
Adjust the screw at the BAC to lower the idle to the desired level.
Throttle cable tension can be holding the throttle body open. Loosen it so it is just slack at idle.
The throttle body stop will increase idle speed if improperly adjusted.
Do not adjust the air mixture screw on the pasenger strut tower.
Hopefully it's just an adjustment not part replacement. Good Luck.
You may want to unplug it and see if it makes a difference. If it doesn't go full rich, consider a replacement.
For searching idle, try setting the throttle position sensor first.
Next check your BAC valve. With the engine running, unplug it and the clicking should stop.
For lowering the idle, check for vacuum leaks that are causing the idle to run high.
Adjust the screw at the BAC to lower the idle to the desired level.
Throttle cable tension can be holding the throttle body open. Loosen it so it is just slack at idle.
The throttle body stop will increase idle speed if improperly adjusted.
Do not adjust the air mixture screw on the pasenger strut tower.
Hopefully it's just an adjustment not part replacement. Good Luck.
04-29-09, 05:07 PM
#3
Full Member
Thread Starter
Join Date: Aug 2005
Location: Cairns, Australia
Posts: 83
Likes: 0
Received 0 Likes
on
0 Posts
I have a spare O2 sensor here but it's my understanding the O2 sensor only makes minor adjustments while actually driving not at idle - I thought that was the AFMs job?
Tried setting the TPS, seemed to make it worse rather than better, but I might have another look at it. I'm thinking it's a BAC issue more than anything else since it steadies out with the AC. It's just rather strange it also steadies out when the clutch is engaged.
The throttle cable seems fine, but I'll check it again maybe chuck some WD-40 on there to see if it's a bit tight.
I've checked all over the shop for vacuum leaks and I can't find any specifically, so I'm just going to replace all the vacuum lines with silicone lines and hope that my problem gets solved there.
The fuel usage really is ridiculous, so I'd like to get it solved :/ could it be a bad ECU maybe? Or a bad FCD?
Tried setting the TPS, seemed to make it worse rather than better, but I might have another look at it. I'm thinking it's a BAC issue more than anything else since it steadies out with the AC. It's just rather strange it also steadies out when the clutch is engaged.
The throttle cable seems fine, but I'll check it again maybe chuck some WD-40 on there to see if it's a bit tight.
I've checked all over the shop for vacuum leaks and I can't find any specifically, so I'm just going to replace all the vacuum lines with silicone lines and hope that my problem gets solved there.
The fuel usage really is ridiculous, so I'd like to get it solved :/ could it be a bad ECU maybe? Or a bad FCD?
05-01-09, 03:49 PM
#4
Forgot to ask. Has the high idle/fuel problem suddenly started or has it always been like this/ gotten progressively worse?
And your startup is the standard 3000 rpm 'accelerated warmup' written into the stock ECU. If you want to eliminate it, start it with the car in gear and step on the clutch. Usually it takes a good 5 minutes before my idle drops from 1500 to 750 due to the stock thermowax system. But your stays at 1200~1500 all the time?
I *think* the ecu takes in both oxygen sensor and AFM readings to determine fuel needs. Hopefully swapping the spare will take care of it. When my oxygen sensor wire broke, my car went full rich to the point that I thought I blew out my new cat.
I'm agreeing with you that your BAC is probably suspect since your idle does not increase when you turn on the A/C. If it's broken, it's probably always off and not clicking. Try unplugging it to see if the clicking sound stops.
People who have eliminated the BAC adjust the idle using the throttle stop screw instead. So it can be done without a BAC. Also, check the thermowax to see if it is stuck or mis-adjusted and holding the throttle open when it is warm.
I don't think the ECU would fail in this manner, but stranger things have happened.
I reallly don't think it is the FCD because it's only a voltage clamp on the boost sensor. It may have failed physically / shorted and is constantly sending a high reading to the ECU. Unplugging it should be an easy test.
I think you've identified most of the places it can go wrong, so hopefully you can start with the easy cheap stuff and work your way up.
And your startup is the standard 3000 rpm 'accelerated warmup' written into the stock ECU. If you want to eliminate it, start it with the car in gear and step on the clutch. Usually it takes a good 5 minutes before my idle drops from 1500 to 750 due to the stock thermowax system. But your stays at 1200~1500 all the time?
I *think* the ecu takes in both oxygen sensor and AFM readings to determine fuel needs. Hopefully swapping the spare will take care of it. When my oxygen sensor wire broke, my car went full rich to the point that I thought I blew out my new cat.
I'm agreeing with you that your BAC is probably suspect since your idle does not increase when you turn on the A/C. If it's broken, it's probably always off and not clicking. Try unplugging it to see if the clicking sound stops.
People who have eliminated the BAC adjust the idle using the throttle stop screw instead. So it can be done without a BAC. Also, check the thermowax to see if it is stuck or mis-adjusted and holding the throttle open when it is warm.
I don't think the ECU would fail in this manner, but stranger things have happened.
I reallly don't think it is the FCD because it's only a voltage clamp on the boost sensor. It may have failed physically / shorted and is constantly sending a high reading to the ECU. Unplugging it should be an easy test.
I think you've identified most of the places it can go wrong, so hopefully you can start with the easy cheap stuff and work your way up.
05-02-09, 08:24 PM
#5
Full Member
Thread Starter
Join Date: Aug 2005
Location: Cairns, Australia
Posts: 83
Likes: 0
Received 0 Likes
on
0 Posts
It's always been like this since I had the car, adjusting the TPS seemed to make it do the 1200-1500 rpm surge though, before I adjusted it it idled at 1500RPM all the time. It's always used an excessive amount of fuel for the entire time I've had it.
I know the 3000RPM thing is a cold start system, but even with clutch put in it still jumps up there and immediately drops down, sometimes it gets to 2000 and then drops down which is rather strange and leads me to think it may just be permanently stuck in cold start mode which my understanding is by default dumps a shitload of extra fuel in there to warm it up.
I have a spare AFM and O2 sensor fortunately enough, might swap in both and see how I go.
The BAC valve appears to be working since when I engage the A/C the idle drops to a dead steady 1000RPM, so I don't think the BAC is the problem. However with A/C on I don't know if this is normal, but I lose 90% of the power in the car, it's like driving a caterpillar.
The boost sensor has had the nipple snapped and was completely disconnected from vac lines when I got the car, I manufactured a new nipple and used a shitload of insulation tape to get it to hold vacuum, this may be causing the problem but it seems to be working fine. Trying to locate a new one since the only spare I have is an S5 and I'm S4.
I should remove the cold start thermowax and see if that helps with anything, but since that is a pretty major job I would rather avoid doing that since the 7 is my DD and the thermowax will be probably a 2 day job. I will probably remove it when I redo my vacuum lines which will happen in the next couple of weeks.
Will try metering the AFM and O2 sensor and seeing if they're working ok before I swap them out since an AFM is getting expensive these days I'd rather have a spare for when it does completely fail, if this is the time, well it's good I have one.
Thanks,
Sean
I know the 3000RPM thing is a cold start system, but even with clutch put in it still jumps up there and immediately drops down, sometimes it gets to 2000 and then drops down which is rather strange and leads me to think it may just be permanently stuck in cold start mode which my understanding is by default dumps a shitload of extra fuel in there to warm it up.
I have a spare AFM and O2 sensor fortunately enough, might swap in both and see how I go.
The BAC valve appears to be working since when I engage the A/C the idle drops to a dead steady 1000RPM, so I don't think the BAC is the problem. However with A/C on I don't know if this is normal, but I lose 90% of the power in the car, it's like driving a caterpillar.
The boost sensor has had the nipple snapped and was completely disconnected from vac lines when I got the car, I manufactured a new nipple and used a shitload of insulation tape to get it to hold vacuum, this may be causing the problem but it seems to be working fine. Trying to locate a new one since the only spare I have is an S5 and I'm S4.
I should remove the cold start thermowax and see if that helps with anything, but since that is a pretty major job I would rather avoid doing that since the 7 is my DD and the thermowax will be probably a 2 day job. I will probably remove it when I redo my vacuum lines which will happen in the next couple of weeks.
Will try metering the AFM and O2 sensor and seeing if they're working ok before I swap them out since an AFM is getting expensive these days I'd rather have a spare for when it does completely fail, if this is the time, well it's good I have one.
Thanks,
Sean
Thread
Thread Starter
Forum
Replies
Last Post
