Lean surge at part throttle
11-28-11, 10:42 AM
#1
Lean surge at part throttle
Hey peeps. I finally got a WB on my car and can see what the AFRs are doing. Well, the car has always had a part throttle surge at really low throttle and speeds, and especially when the car is cold.
Anywho, with the WB, I can now see that when it surges, the AFRs spike to as high as 18:1. Could an old O2 sensor be the issue here? AFAIK, I am still running the original 100k mile Aristo sensor. I have another one to try, and plan to as soon as I can. Is there anything else I can check out?
FYI, when I am WOT and in boost, AFRs come down to the 11-11.5:1 range. Idle and warm cruise are around 15-15.5:1 as expected.
Anywho, with the WB, I can now see that when it surges, the AFRs spike to as high as 18:1. Could an old O2 sensor be the issue here? AFAIK, I am still running the original 100k mile Aristo sensor. I have another one to try, and plan to as soon as I can. Is there anything else I can check out?
FYI, when I am WOT and in boost, AFRs come down to the 11-11.5:1 range. Idle and warm cruise are around 15-15.5:1 as expected.
12-07-11, 04:50 PM
#7
Man I think I screwed it up worse. It MUST be the tps. I adjusted it and thought I had it, but now its actually worse. 
Since it changed, it must be the issue. I will attempt the adjustment again this weekend.
The more I think about it, the more tps makes sense. When the car is cold, it should be in open loop. The O2 should be ignored until the car is up to whatever temp threshold determines closed loop, so I would bet the tps and map are all the ecu uses for fueling.
Once the car warms up, the issue seems to go away, which tells me O2 feedback is correcting the fueling... I will report back what I figure out.
Since it changed, it must be the issue. I will attempt the adjustment again this weekend. The more I think about it, the more tps makes sense. When the car is cold, it should be in open loop. The O2 should be ignored until the car is up to whatever temp threshold determines closed loop, so I would bet the tps and map are all the ecu uses for fueling.
Once the car warms up, the issue seems to go away, which tells me O2 feedback is correcting the fueling... I will report back what I figure out.
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12-09-11, 12:38 PM
#9
Hmmmm, I don't get it. I double checked the TPS today and it is perfect according tot he tsrm. All resistance readings are in range and it has a solid, full range of motion with linear resistance increase as it should.
The car still does the stupid lean surge until its warm, and then it runs great. I am confused.
If I try to pedal through the lean spot when its cold, I can pretty much modulate the throttle through 75% without it ever responding. It will just bog, buck and read lean. If I go WOT, it starts to dump the fuel and the car pulls normally.
Its like the throttle is in binary on/off mode with nothing between 0 and WOT. Once it warms up, I get full, normal response and fueling across the throttle range. WTF Mate?
I guess I will try the O2 after all since I am out of ideas.
The car still does the stupid lean surge until its warm, and then it runs great. I am confused.
If I try to pedal through the lean spot when its cold, I can pretty much modulate the throttle through 75% without it ever responding. It will just bog, buck and read lean. If I go WOT, it starts to dump the fuel and the car pulls normally.
Its like the throttle is in binary on/off mode with nothing between 0 and WOT. Once it warms up, I get full, normal response and fueling across the throttle range. WTF Mate?
I guess I will try the O2 after all since I am out of ideas.
12-10-11, 08:31 PM
#12
The GTE uses heated o2 sensors so they are used sooner than regular o2 sensors.
I would change them out if unsure just cause I have heard bad o2 sensors can really affect how it drives overall.
Normally the stock ecu runs really rich when cold, so I think you may have a different issue if its that lean right after its started.
hows your map sensor? any possible vac leaks?
I think even the coolant temp sensor can have those symptoms when cold.
I would change them out if unsure just cause I have heard bad o2 sensors can really affect how it drives overall.
Normally the stock ecu runs really rich when cold, so I think you may have a different issue if its that lean right after its started.
hows your map sensor? any possible vac leaks?
I think even the coolant temp sensor can have those symptoms when cold.
Last edited by Ali SC3; 12-10-11 at 08:36 PM.
12-11-11, 04:51 AM
#13
Ali, I will check the CTS as well, since I have heard that can also cause the issue. Just to clarify, when it is cold started, it idles up as it is supposed to, and the afr sits between 12 and 13:1. If I let it sit for a few minutes idling, it warms up a little bit and then does lean out at idle and even at idle it will surge. I had not really noticed that until yesterday since I don't usually let it sit so long at idle.
I had to order an O2 yesterday since nobody stocks the dang thing. Even Toyota had to order it, and they wanted $166 for it LOL. Found a new one on ebay for $43 shipped.
This situation is where a standalone, piggyback, or OBDII would help so much. Not being able to monitor sensor output realtime makes diagnostics a PITA.
I had to order an O2 yesterday since nobody stocks the dang thing. Even Toyota had to order it, and they wanted $166 for it LOL. Found a new one on ebay for $43 shipped.
This situation is where a standalone, piggyback, or OBDII would help so much. Not being able to monitor sensor output realtime makes diagnostics a PITA.