HELP!! IAT, MAF, Tune??
Thread Starter
Teching In
Joined: Dec 2012
Posts: 10
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From: Las Cruces, NM
HELP!! IAT, MAF, Tune?? Hope this is in the right place. Quick background, super clean 91 with swapped LS1 and M6. ran fine no issues. Recently did heads, cam, LSXRT 102 (RT not R) 102 TB, shorty lifters, trundle kit, 46lb LS2 injectors. Got it tuned at a reputable shop, got it back ran ok at speed except never wanted to idle right. Didnt catch idle would die a lot. Took it back got a little better but same issue just not as bad. repeated this about 3 more times, last time ran much better with the exception of now intermitentaly once warmed up and I believe on warmer days above Id say 45 Degrees (could be coincidence) it will idle at 1600 rpms only when rolling, complete stop for a few seconds it comes down to almost normal, about 900 when should be 800. Typical fixes for dont seem to be the issue. Do have a code P1111(intermitent High voltage at IAT) Could this be my problem? Or could it be the tune however doesnt do it consistantly enough makes me think it is not the tune, but I dont know. going to replace the IAT sensor and connector but could that cause /fix this?already paid over 600 bucks to tune this thing and very hesitant to completely retune just to go through it all again. This idle thing is driving me insane. Desperately need help. Thanks to all
Joined: Aug 2007
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From: Turnin' Wrenches Infractions: 005
Honestly, I've heard horror stories of the 102 TBs and even the 90mm cable driven for being a pain in the butt to tune correctly. As a learning tuner on a few local cars I can tell you honestly getting them to run right at speed is a breeze. Idle is a whole different can of worms. Mine fought an experienced tuner with an LS6 intake and P+P stock TB and MAF. Here's my thoughts.....what MAF are you running, what PCM and harness, what year operating system is in that PCM? No issues before the H/C/I swap? Tuner mention anything about a rolling idle table in your tune? Have you done a TPS reset since the intake/TB install? Idle tuning **** is tricky, there are all kinds of tables that effect it. I've watched tuners fight with that crap for hours trying to get stock like drive-ability.
Thread Starter
Teching In
Joined: Dec 2012
Posts: 10
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From: Las Cruces, NM
Running the stock MAF, fairly confident that its pre 2001 PCM and harness. starting to see some of the same feedback for these 102s. A little much for an NA car.First couple of tunes was fixing te idle now it runs well except for about 75% of the time idles high when rolling like the throttle cracker was adjusted cause its always right at the same rpms, tuner said he set it to zero. So dont know if the IAT could cause that but its the only code showing. With the HP tuners I am hearing that theyre better so might get it retuned here at the local place, thats what they use. last tune i believe was LS1 edit
Thread Starter
Teching In
Joined: Dec 2012
Posts: 10
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From: Las Cruces, NM
Replaced the sensor and connector. Thought that fixed it but eventually started doing it again. May have to suck it up and get it retuned with HP. May be dumb question, fairly new to issues of tunning, however whats the RAF? Yet to hear of that table while looking for solutions to this.
Thread Starter
Teching In
Joined: Dec 2012
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From: Las Cruces, NM
Also really apreciate everyones feedback so far. Main reason i hope its not the tune is ive heard of others having identicle problems on here bonestock but never update how or if they resolved it
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FormerVendor
Joined: Nov 2012
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From: Dyno Tuning in KY
RAF is kinda a crappy acronym for base running airflow. If it were me that came up with it it'd be BRA instead of RAF (Running Air Flow).
Basically the IACV gets its command from the PCM which converts an airflow value into effective area which is then looked up on a table for steps on the IAC. The BRA/RAF is the foundation or starting point for the idle control system to base off of. There are other adders such as cooling fan airflow and startup airflow etc that add to the base to get a desired airflow. Then you have a PID system that controls the idle airflow with a PID control algorithm. P stands for proportional, I stands for integral and D stands for derivative. These 3 methods of idle control add or subtract airflow from the desired airflow to keep idle stable or close to the commanded idle rpm.
Basically what I meant by all of that is if you have too much BRA/RAF when you are rolling at speed the IAC will be open too far and will cause the car to hang at a higher RPM. Once rolling the PID control is disabled and the IAC runs off of BRA/RAF + Throttle cracker if throttle is closed and uses Throttle Follower if the throttle is open. This also varies some between operating systems and platforms cause some corvettes don't use all the functions I mension above.
Basically the IACV gets its command from the PCM which converts an airflow value into effective area which is then looked up on a table for steps on the IAC. The BRA/RAF is the foundation or starting point for the idle control system to base off of. There are other adders such as cooling fan airflow and startup airflow etc that add to the base to get a desired airflow. Then you have a PID system that controls the idle airflow with a PID control algorithm. P stands for proportional, I stands for integral and D stands for derivative. These 3 methods of idle control add or subtract airflow from the desired airflow to keep idle stable or close to the commanded idle rpm.
Basically what I meant by all of that is if you have too much BRA/RAF when you are rolling at speed the IAC will be open too far and will cause the car to hang at a higher RPM. Once rolling the PID control is disabled and the IAC runs off of BRA/RAF + Throttle cracker if throttle is closed and uses Throttle Follower if the throttle is open. This also varies some between operating systems and platforms cause some corvettes don't use all the functions I mension above.
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Verdad Gallardo Thread Starter
Teching In
Joined: Dec 2012
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From: Las Cruces, NM
Alright. Good explanation, all made sense. Now however even if any of that we're the case wouldn't it do it consistantly if in the tune like that. I only ask because its very intermittent. It seems to only do it once warmed up and once it starts sometimes will last for even an hour drive (most times) and sometimes will just last for a couple lights,Now if I I force the Rpms down like say lug it down by putting it in a high gear rolling slower it will bring it down and as long as I put in neutral below 1k it'll stay down. Still a bit high but not the 1600
FormerVendor
Joined: Nov 2012
Posts: 390
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From: Dyno Tuning in KY
It's really hard to say. Timing plays a large roll in rpm as well. I've seen higher timing at rpm cause the rpm to hang. There's a lot of things going on in the idle routine that must jive together to operate correctly.
Has any of the trouble codes come back since you replaced the sensor and plug?
Has any of the trouble codes come back since you replaced the sensor and plug?
