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LQ1 Fast Idle between shifts and at slow role by CC Rider
Started on: 03-04-2013 09:23 PM
Replies: 11 (304 views)
Last post by: Darth Fiero on 02-20-2014 05:15 PM
CC Rider
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Report this Post03-04-2013 09:23 PM Click Here to See the Profile for CC RiderClick Here to Email CC RiderSend a Private Message to CC RiderEdit/Delete MessageReply w/QuoteDirect Link to This Post

On my 3.4 DOHC manual swap I’m having a problem with the TB?
When coming to a stop, with the clutch in, my engine is at ~1500 rpm’s until I stop. Once stopped it drops to 1000 rpm’s.
I'm also noticing that during shifts the RPM hangs and doesn’t drop to what I think it should for the next gear.
Have checked the spring on the TB and it looks and feels like it should. Replaced the TPS and cleaned and adjusted the IAC. No change No codes?

Any suggestion would be great - thanks

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Red 1988 GT 5 speed
Poly all around, Koni's & Lowered
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3800 swap in progress
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The Aura
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Report this Post03-04-2013 09:53 PM Click Here to See the Profile for The AuraClick Here to Email The AuraSend a Private Message to The AuraEdit/Delete MessageReply w/QuoteDirect Link to This Post
I believe the automatics have it built into the programming to idle slightly higher at speed over anything but zero.
What Chip do you have? Perhaps it hasn''t been removed from the programming to suit your manual transmission.

[This message has been edited by The Aura (edited 03-04-2013).]

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sspeedstreet
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Report this Post03-04-2013 10:45 PM Click Here to See the Profile for sspeedstreetClick Here to Email sspeedstreetSend a Private Message to sspeedstreetEdit/Delete MessageReply w/QuoteDirect Link to This Post
Yep, mine is the same way and I really don't like it. Apparently this is how GM "fixed" the engine dying problem when you go off-throttle. Mine was bad enough with the stock BFCA chip (It dropped to idle at about 1500 rpm because it was reading the Fiero speedo sender). I had Darth do me a new chip with a few tweeks and while he was at it he corrected the pulse count. Now it acts just like you describe. He offered to try masking over the the off-throttle with the automatic chip's program, but I never followed through on it.

If you come up with a fix, let me know,

Neil
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ls3mach
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Report this Post03-04-2013 11:05 PM Click Here to See the Profile for ls3machSend a Private Message to ls3machEdit/Delete MessageReply w/QuoteDirect Link to This Post
I think they have it right. My 5spd LQ1 had to be pulled out of gear or blip the throttle otherwise it would die. It was a manual vs auto issue. Get with Darth, he seems to be the man.

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Darth Fiero
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Report this Post03-04-2013 11:10 PM Click Here to See the Profile for Darth FieroClick Here to visit Darth Fiero's HomePageClick Here to Email Darth FieroSend a Private Message to Darth FieroEdit/Delete MessageReply w/QuoteDirect Link to This Post
The manual trans programming has that "fast idle hang" characteristic built into it from the factory. It could very well have been put in there by GM to prevent stalling issues.

If you want, you can send me the chip and I can try lowering it for you - but I cannot guarantee it will work as desired as it could cause other issues (ie: such as stalling).

But there are things we can try.

-ryan

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Fierobsessed
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Report this Post03-05-2013 08:44 AM Click Here to See the Profile for FierobsessedClick Here to Email FierobsessedSend a Private Message to FierobsessedEdit/Delete MessageReply w/QuoteDirect Link to This Post
Which engine management are you running? 91-93 I assume? Is your clutch switch connected and working correctly?
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CC Rider
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Report this Post03-05-2013 08:57 AM Click Here to See the Profile for CC RiderClick Here to Email CC RiderSend a Private Message to CC RiderEdit/Delete MessageReply w/QuoteDirect Link to This Post
This is all great info and glad I'm not the only one having the issue because I was running out of ideas and cash to throw at the issue.
On long trips and hot daysI have a stalling issue from time to time. Have to turn on the AC to compensate but is doesn't always work.

I'll be in touch Ryan in a few weeks.
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CC Rider
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Report this Post03-05-2013 09:01 AM Click Here to See the Profile for CC RiderClick Here to Email CC RiderSend a Private Message to CC RiderEdit/Delete MessageReply w/QuoteDirect Link to This Post

CC Rider

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quote
Originally posted by Fierobsessed:

Which engine management are you running? 91-93 I assume? Is your clutch switch connected and working correctly?


OBD1 and yes the clutch switch is connected.
No code since the install years ago.
Have close to 40k on the swap.
Can you explaine why you asked these question?
I'd like to know what you know please.

Thanks

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Fierobsessed
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Report this Post03-05-2013 11:14 AM Click Here to See the Profile for FierobsessedClick Here to Email FierobsessedSend a Private Message to FierobsessedEdit/Delete MessageReply w/QuoteDirect Link to This Post
Nothing really, I just wasn't sure if you were 91-93 management, or 94-95. I've been running a manual with a modified 94-95 code (auto delete) and have been very pleased with it. But it too holds a slightly higher idle till I come to a stop.

I'm not totally sure what the clutch switch controls, but I would venture to guess it would have to do with closed loop idle control somehow.

I raised the threshold for Max MPH for Closed loop idle to 20 just to see how it felt on my 94-95. It had a side effect when in first gear at low speeds, the car would start bucking heavily, but it did allow a low idle long before coming to a stop. I'd be more helpful if you were 94-95.
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Darth Fiero
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Report this Post03-05-2013 04:24 PM Click Here to See the Profile for Darth FieroClick Here to visit Darth Fiero's HomePageClick Here to Email Darth FieroSend a Private Message to Darth FieroEdit/Delete MessageReply w/QuoteDirect Link to This Post
It is worth noting the differences between the computer systems...

1991-93 3.4 DOHC computers are speed density and will work with ANY 3.4 DOHC engine, regardless of what year it is. These PCMs were used in factory applications that came with 4T60-E auto transmissions or 5-speed manual transmissions. These PCMs have removable mem-cals/chips.

1994-95 3.4 DOHC computers work in SFI mode, use a MAF sensor and will only work with 1994-newer 3.4 DOHC engines because of the need for the additional crank sensor (24x) and cam sensor (1x). GM discontinued the use of the 5-speed manual transmissions with 3.4 DOHC engines after 1993 model year so this PCM and the later OBD2 systems were only used with automatics. This PCM can control a 4T60-E auto or it can work with a manual trans if custom programmed for it. These PCMs have removable mem-cals/chips.

1996 3.4 DOHC SFI OBD2 PCMs use MAF and MAP sensors, and will work with a 4T60-E auto trans (or manual trans if custom programmed for it). These PCMs must be reflashed to be reprogrammed, and will only work with 1994-newer 3.4 DOHC engines because of the need for the additional crank sensor (24x) and cam sensor (1x).

1997 3.4 DOHC SFI OBD2 PCMs use MAF and MAP sensors, and will work with a 4T65-E auto trans (or manual trans if custom programmed for it). These PCMs must be reflashed to be reprogrammed, and will only work with 1994-newer 3.4 DOHC engines because of the need for the additional crank sensor (24x) and cam sensor (1x).

-ryan

[This message has been edited by Darth Fiero (edited 03-05-2013).]

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CC Rider
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Report this Post02-20-2014 11:40 AM Click Here to See the Profile for CC RiderClick Here to Email CC RiderSend a Private Message to CC RiderEdit/Delete MessageReply w/QuoteDirect Link to This Post
Been thinking about putting a VSS kill switch on the clutch pedal.
Do you see any problems that this may cause?
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Darth Fiero
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Report this Post02-20-2014 05:15 PM Click Here to See the Profile for Darth FieroClick Here to visit Darth Fiero's HomePageClick Here to Email Darth FieroSend a Private Message to Darth FieroEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by CC Rider:

Been thinking about putting a VSS kill switch on the clutch pedal.
Do you see any problems that this may cause?


Yes, killing the VSS signal unexpectedly can give the ECM fits. Have you had the chip reprogrammed to try to lower the fast idle hang problem yet? If not, I would try that first.
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