idle issues
11-15-2009, 04:38 PM
#1
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Thread Starter
Join Date: Jun 2009
Posts: 72
idle issues
First of all I just finished having Ai's 226/234 cam, TCI 3200-3400 stall, AFR 180cc heads, a 58 mm throttle body, edlebrock intake, and a mail ordered tune put in my 93 z28.
Sometimes when I start my car it will idle around 500 rpm then die, unless I rev it to about 1000 rpm for a few seconds. Then one day I was driving to work and I believe I was in 4th gear when I let of the gas. After coasting for a few seconds my rpm dropped to about 500, and my car felt like it was going to die. So I revved it up and it was alright, but the check engine light came on for a couple of seconds. My mechanic decoded it for me and said it was a high voltage MAP code.
I'm not sure if it was related to the tune or somthing else. I just wanted to see if anybody had any ideas.
Sometimes when I start my car it will idle around 500 rpm then die, unless I rev it to about 1000 rpm for a few seconds. Then one day I was driving to work and I believe I was in 4th gear when I let of the gas. After coasting for a few seconds my rpm dropped to about 500, and my car felt like it was going to die. So I revved it up and it was alright, but the check engine light came on for a couple of seconds. My mechanic decoded it for me and said it was a high voltage MAP code.
I'm not sure if it was related to the tune or somthing else. I just wanted to see if anybody had any ideas.
11-15-2009, 09:54 PM
#2
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Join Date: Nov 1998
Location: Hell was full so they sent me to NJ
Posts: 70,671
High MAP corresponds to low vacuum. The code only sets when the MAP goes above 68kPA, and the TPS indicates less than 4% throttle opening. Indicates a problem with manifold vacuum. First guess would be a vacuum leak... but you have low idle, which indicates the engine isn't getting enough air. Possibly you have misadjusted valves causing high manifold pressure. Or its misfiring so badly at idle there is insufficient vacuum.
The IAC motor should open up to add enough air to keep the idle speed where it's programmed. What idle speed did the tuner set it for?
Are you aware you can "decode" your 93 simply by shorting the ALDL pins and flashing the codes on your SES light, then looking them up. Shoebox has the info you need:
http://shbox.com/1/dlc2.jpg
http://shbox.com/1/Dtcs.htm
Note that some of the 93 DTC's are different than other years. The 93 codes on on the far right column on the page I linked.
The IAC motor should open up to add enough air to keep the idle speed where it's programmed. What idle speed did the tuner set it for?
Are you aware you can "decode" your 93 simply by shorting the ALDL pins and flashing the codes on your SES light, then looking them up. Shoebox has the info you need:
http://shbox.com/1/dlc2.jpg
http://shbox.com/1/Dtcs.htm
Note that some of the 93 DTC's are different than other years. The 93 codes on on the far right column on the page I linked.
11-16-2009, 02:37 PM
#3
Registered User
Thread Starter
Join Date: Jun 2009
Posts: 72
High MAP corresponds to low vacuum. The code only sets when the MAP goes above 68kPA, and the TPS indicates less than 4% throttle opening. Indicates a problem with manifold vacuum. First guess would be a vacuum leak... but you have low idle, which indicates the engine isn't getting enough air. Possibly you have misadjusted valves causing high manifold pressure. Or its misfiring so badly at idle there is insufficient vacuum.
The IAC motor should open up to add enough air to keep the idle speed where it's programmed. What idle speed did the tuner set it for?
Are you aware you can "decode" your 93 simply by shorting the ALDL pins and flashing the codes on your SES light, then looking them up. Shoebox has the info you need:
http://shbox.com/1/dlc2.jpg
http://shbox.com/1/Dtcs.htm
Note that some of the 93 DTC's are different than other years. The 93 codes on on the far right column on the page I linked.
The IAC motor should open up to add enough air to keep the idle speed where it's programmed. What idle speed did the tuner set it for?
Are you aware you can "decode" your 93 simply by shorting the ALDL pins and flashing the codes on your SES light, then looking them up. Shoebox has the info you need:
http://shbox.com/1/dlc2.jpg
http://shbox.com/1/Dtcs.htm
Note that some of the 93 DTC's are different than other years. The 93 codes on on the far right column on the page I linked.
I was just reading another post and I saw that if your throttle body is open to much it could throw off the IAC. Do you think this could be the problem?
-Edit- Checked the voltage on the tps, and it was around .79.
Thanks for the help.
Last edited by TM2S3; 11-16-2009 at 04:36 PM.
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