Rough idle and stumble when in closed loop
Thread Starter
Instructor
Joined: Dec 2012
Posts: 120
Likes: 1
From: Canton Georgia
Rough idle and stumble when in closed loop
I've got a 1986 c4 corvette with an 87 l98 with long tube headers. I've gotten the engine tuned with pcm for less im using a heated Bosch 13077 02 sensor stock maf. No codes its totally fine when its cold but once is warms up it runs like crap. Im going to put my scanner on it to see if the tps voltage is bad and i might swap maf's. I have a feeling it could be the o2 sensor but which o2 sensor should i use if this one wont work? I know im posting a alot but i just gotta get this thing finished.
Melting Slicks
Joined: Jun 2013
Posts: 3,065
Likes: 39
I've got a 1986 c4 corvette with an 87 l98 with long tube headers. I've gotten the engine tuned with pcm for less im using a heated Bosch 13077 02 sensor stock maf. No codes its totally fine when its cold but once is warms up it runs like crap. Im going to put my scanner on it to see if the tps voltage is bad and i might swap maf's. I have a feeling it could be the o2 sensor but which o2 sensor should i use if this one wont work? I know im posting a alot but i just gotta get this thing finished.
Do you have a chip burner? I can take a look at your tune and might be able to change some things to improve the problem.
Thread Starter
Instructor
Joined: Dec 2012
Posts: 120
Likes: 1
From: Canton Georgia
I don't think its the tune. I drove it with the stock tune for a while and it was doing the same thing. The new tune helped it not to run so lean on the top end but there is for sure something not right. Rough idle is when warmed up it hunts around from 6-900 rpm. In drive the car lurches forward on its own if you just sit there with the brakes on. When your actually driving its weird because you give it a little gas and it doesn't do much then you give it a little more and it goes wild like theres a deadspot? Also if your just crusing around 25 miles an hour like getting back into my neighborhood the car goes down to about 400 rpm and almost dies in drive without me using the brakes or any throttle.
Last edited by sansonic; May 12, 2014 at 02:42 PM.
Melting Slicks
Joined: Jun 2013
Posts: 3,065
Likes: 39
I don't think its the tune. I drove it with the stock tune for a while and it was doing the same thing. The new tune helped it not to run so lean on the top end but there is for sure something not right. Rough idle is when warmed up it hunts around from 6-900 rpm. In drive the car lurches forward on its own if you just sit there with the brakes on. When your actually driving its weird because you give it a little gas and it doesn't do much then you give it a little more and it goes wild like theres a deadspot? Also if your just crusing around 25 miles an hour like getting back into my neighborhood the car goes down to about 400 rpm and almost dies in drive without me using the brakes or any throttle.
1987 was the start of the roller camshaft, which has different lobe profiles which could be the cause of your idle surge.
I would start out with a stock 87 tune and base it off of that. Or you can even load a stock 87 and just try it out.
If you already have that done, then I would look into what your TPS voltage is at idle.
And it kinda throws it towards the tune or the O2 sensor when you say it happens only in Closed Loop. Which is why I'm leaning in the direction of the tune.
Are you sure it isn't temperature specific? If you unplug the O2 sensor when it warmed up and take it for a 15 minute drive, does it still do that?
Thread Starter
Instructor
Joined: Dec 2012
Posts: 120
Likes: 1
From: Canton Georgia
Did you start off with a stock 87 tune instead of a stock 86 tune?
1987 was the start of the roller camshaft, which has different lobe profiles which could be the cause of your idle surge.
I would start out with a stock 87 tune and base it off of that. Or you can even load a stock 87 and just try it out.
If you already have that done, then I would look into what your TPS voltage is at idle.
And it kinda throws it towards the tune or the O2 sensor when you say it happens only in Closed Loop. Which is why I'm leaning in the direction of the tune.
Are you sure it isn't temperature specific? If you unplug the O2 sensor when it warmed up and take it for a 15 minute drive, does it still do that?
1987 was the start of the roller camshaft, which has different lobe profiles which could be the cause of your idle surge.
I would start out with a stock 87 tune and base it off of that. Or you can even load a stock 87 and just try it out.
If you already have that done, then I would look into what your TPS voltage is at idle.
And it kinda throws it towards the tune or the O2 sensor when you say it happens only in Closed Loop. Which is why I'm leaning in the direction of the tune.
Are you sure it isn't temperature specific? If you unplug the O2 sensor when it warmed up and take it for a 15 minute drive, does it still do that?
Melting Slicks
Joined: Jun 2013
Posts: 3,065
Likes: 39
I started with the 87 tune ive got a wrecked 87 that i took the computer out of and used. Im going to run the scanner tommorow when i take it to a shop to have them fix this transmission leak ive been battling for a while. I'll try to unplug the o2 sensor and see. I gotta check if the o2 cross counts are reading or not. I think the tps may be fine cause when i first start it up this thing is a monster it will seriously roast the tires. I was hoping the tune would cure the problem all together it only seemed to help it a little.
Melting Slicks
Joined: Aug 2008
Posts: 2,082
Likes: 50
From: Palmdale CA
I recently had similar symptoms on my Honda when I installed a Bosch 02 sensor, I swapped it out for an Denso 02 sensor and my problems were gone, my problem was so bad I almost couldn't drive the car!
Having said this, when I did my top end (95) a couple years back I installed Bosch on both sides without issue.. just a thought!
Having said this, when I did my top end (95) a couple years back I installed Bosch on both sides without issue.. just a thought!
Thread Starter
Instructor
Joined: Dec 2012
Posts: 120
Likes: 1
From: Canton Georgia
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
Melting Slicks
Joined: Jun 2013
Posts: 3,065
Likes: 39
Thread Starter
Instructor
Joined: Dec 2012
Posts: 120
Likes: 1
From: Canton Georgia
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
Thread Starter
Instructor
Joined: Dec 2012
Posts: 120
Likes: 1
From: Canton Georgia
Finally got it back from the shop and ran the scanner on it. it has 1 o2 cross count and it stays like that the whole time same with just the regular o2 reader. Seems like my o2 sensor may have been DOA. It could also be a wiring problem. Im going to try and drive it with the o2 sensor unplugged. Is this the correct heated o2 sensor to use?
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
There should be an O2 sensor voltage reading in your scan somewhere. The voltage should vary between about 0.2 and 0.8 volts (it might be shown in millivolts, in which case it would be 200 to 800 mV). Please post your O2 sensor voltage.
Some O2 sensors (especially wideband sensors) have a wider voltage range, up to around 3 volts. The response curve for a wideband O2 sensor is completely different also. They will not work on your car if connected directly to the ECM. There are converter boxes that will convert the wideband O2 sensor output to one that is compatible with the ECM.
Some O2 sensors (especially wideband sensors) have a wider voltage range, up to around 3 volts. The response curve for a wideband O2 sensor is completely different also. They will not work on your car if connected directly to the ECM. There are converter boxes that will convert the wideband O2 sensor output to one that is compatible with the ECM.
Thread Starter
Instructor
Joined: Dec 2012
Posts: 120
Likes: 1
From: Canton Georgia
There should be an O2 sensor voltage reading in your scan somewhere. The voltage should vary between about 0.2 and 0.8 volts (it might be shown in millivolts, in which case it would be 200 to 800 mV). Please post your O2 sensor voltage.
Some O2 sensors (especially wideband sensors) have a wider voltage range, up to around 3 volts. The response curve for a wideband O2 sensor is completely different also. They will not work on your car if connected directly to the ECM. There are converter boxes that will convert the wideband O2 sensor output to one that is compatible with the ECM.
Some O2 sensors (especially wideband sensors) have a wider voltage range, up to around 3 volts. The response curve for a wideband O2 sensor is completely different also. They will not work on your car if connected directly to the ECM. There are converter boxes that will convert the wideband O2 sensor output to one that is compatible with the ECM.
My readings are:
0.55 throttle position
160 iac present position
127.40 coolant temp
00 vehicle speed
0.00 egr duty cycle
(600) changes: engine speed
(128) changes: base pulse correction
1096.68 does not change: 02
10 knock count
(128) blm runs rich so goes down to 108 and back
(01) 02 cross counts does not change
(26264) changes: airflow
(83.00) changes: base pulse width
enabled learn control
Rich rich/lean
closed loop status
off shift light.
Le Mans Master
Joined: Aug 2007
Posts: 8,735
Likes: 412
From: WV
It should be either the O2 sensor is bad , or the wiring/connection is bad . I would check to see how much voltage your getting going to the sensor.. If it's not that it should be a bad O2 sensor...When reading with the scanner the O2 sensor reading should be constantly jumping to different numbers.. It's never suppose to stay on 1 number..The BLM running rich is most likely because of the O2 sensor imput being wrong......WW
Last edited by WW7; May 22, 2014 at 10:15 AM.
Thread Starter
Instructor
Joined: Dec 2012
Posts: 120
Likes: 1
From: Canton Georgia
It should be either the O2 sensor is bad , or the wiring/connection is bad . I would check to see how much voltage your getting going to the sensor.. If it's not that it should be a bad O2 sensor...When reading with the scanner the O2 sensor reading should be constantly jumping to different numbers.. It's never suppose to stay on 1 number..The BLM running rich is most likely because of the O2 sensor imput being wrong......WW
Le Mans Master
Joined: Aug 2007
Posts: 8,735
Likes: 412
From: WV
....WW
Last edited by WW7; May 22, 2014 at 11:38 AM.
Drifting
Joined: May 2013
Posts: 1,736
Likes: 31
From: Reno Nevada
Im using tunerpro rt and i can provide the file if you need it. Just let me know which file host to use.
My readings are:
0.55 throttle position
160 iac present position
127.40 coolant temp
00 vehicle speed
0.00 egr duty cycle
(600) changes: engine speed
(128) changes: base pulse correction
1096.68 does not change: 02
10 knock count
(128) blm runs rich so goes down to 108 and back
(01) 02 cross counts does not change
(26264) changes: airflow
(83.00) changes: base pulse width
enabled learn control
Rich rich/lean
closed loop status
off shift light.
My readings are:
0.55 throttle position
160 iac present position
127.40 coolant temp
00 vehicle speed
0.00 egr duty cycle
(600) changes: engine speed
(128) changes: base pulse correction
1096.68 does not change: 02
10 knock count
(128) blm runs rich so goes down to 108 and back
(01) 02 cross counts does not change
(26264) changes: airflow
(83.00) changes: base pulse width
enabled learn control
Rich rich/lean
closed loop status
off shift light.
Thread Starter
Instructor
Joined: Dec 2012
Posts: 120
Likes: 1
From: Canton Georgia
If you find out it's the sensor that's bad, I would just get a new sensor.. If your using a heated sensor you must need it... Are you sure you hooked it up correctly when you installed it by running the hot wire on the sensor to a "key on" hot wire??.It could very well be just a bad sensor, you wouldn't believe the number of defective "NEW" parts I have purchased.......WW
....WW
Thread Starter
Instructor
Joined: Dec 2012
Posts: 120
Likes: 1
From: Canton Georgia
So good news and bad news. Good news o2 sensor was wired incorrectly now its reading and the low stumble is gone. Bad news. The car now idles at 1000 rpm which is a little odd it wasnt doing that before. And on my scanner it looks like its running lean because the blms are high it also had a huge knock count of like 64 so im assuming its to lean. Not to worry i didnt hurt the motor i run 93 octane and wasnt beating on it to hard.
My new question is do i need a different tune or an adjustable fuel pressure regulator? And i guess i just need to do the idle reset procedure and should i reset the computer now that i got the o2 sensor working?
My new question is do i need a different tune or an adjustable fuel pressure regulator? And i guess i just need to do the idle reset procedure and should i reset the computer now that i got the o2 sensor working?