Motor swap, mustang revs up on its own help?

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lowrybl

New Member

Feb 18, 2011

6

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0

Apr 28, 2011

#1

• Apr 28, 2011

• #1

Just swapped a motor from a 98 gt into mine. Just bolted it up and started the car. car starts fine, idles fine for a few seconds, then will rev up close to 2k rpm. It was a full motor swap, npi shortblock, pi heads, comp 270 cams, edelbrock victor jr intake, edelbrock fuel rails. Tried a new computer, didnt work. tps seems to be fine. O2 sensors are showing pegged out in volts? did i pinch the harness or something putting the motor in?

 

N8Dogg98

15 Year Member

Apr 4, 2005

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MN

Apr 28, 2011

#2

• Apr 28, 2011

• #2

It could be the IAC.

 

9

93 331 GT

Member

Mar 5, 2006

60

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7

Jackson, NJ

Apr 28, 2011

#3

• Apr 28, 2011

• #3

Check the TPS on throttle body. I had the same issue about six months ago. Changed everything before finding it. Take it off and use a large flat head screw driver to turn it slowly if it doesnt spring right back thats your problem.

 

txstang84

15 Year Member

May 21, 2005

1,639

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Tuscola, tx

Apr 28, 2011

#4

• Apr 28, 2011

• #4

There have been two separate [known good] TPSs installed on that TB so far, swapped computers [also good], and still no fix. Volts are stable when KOEO, but KOER TPS spikes from actual voltage/throttle pos + fluxing voltage; e.g. fluxing from 1.4V ~ 1.8V slightly above idle...2.4V ~ 2.8V mid throttle, and so on. Also, O2s as mentioned are pegged....

ttt

 

usaf_branham

15 Year Member

Oct 30, 2008

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84

Boston

Apr 28, 2011

#5

• Apr 28, 2011

• #5

i would initially suspect iac, tps, or vacuum leak. im not saying it couldnt be something else, but that is where i would start.

 

wmburns

SN Certified Technician

Aug 14, 2009

5,892

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204

Houston Texas

Apr 28, 2011

#6

• Apr 28, 2011

• #6

txstang84 said:

There have been two separate [known good] TPSs installed on that TB so far, swapped computers [also good], and still no fix. Volts are stable when KOEO, but KOER TPS spikes from actual voltage/throttle pos + fluxing voltage; e.g. fluxing from 1.4V ~ 1.8V slightly above idle...2.4V ~ 2.8V mid throttle, and so on. Also, O2s as mentioned are pegged....

ttt

Click to expand...

the solution to your problem is in your post (the "fluxing" of the TPS).

With regards to the function of the TPS, the most important thing is a stable closed throttle value. It doesn't matter what the value is as long as it is the same value each time the throttle is closed.

For confirmation, monitor the TP-MODE PID. Is it switching from "C/T" to "P/T"?

Start first by checking the throttle return spring. Is it tight? Next look for loose or wore out throttle linkage.

Check out the following for addtional information:

Is your mustang stumbling, dieing at idle or idling rough? - Page 14 - Ford Mustang Forums

 

txstang84

15 Year Member

May 21, 2005

1,639

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Tuscola, tx

May 10, 2011

#7

• May 10, 2011

• #7

Issue remedied...dirty connectors