Question about 1985 Pontiac Firebird

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85 trans am 305 mpfi rough idle at start

Hello hope youve got the answer
replaced plug+wires cap rotor tps. before the car ran really bad as if it was missing(hot or cold). after cleaning the plenum, replacing iacv,and checked timing, it runs rough during warm up(5 min) instructions(iacv) said to run the car at 40mph for about 20min to reset computer. pulled in the driveway and idled fine for 10 min(not the usual up/down in rpms or stalling like at startup). i still have the same idle issue at start up. im thinking cold start valve or mat sensor in the plenum. your advise is greatly appreciated!!!!!! rich

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  • jimi41 Feb 16, 2009

    my trans am will start fine then run real rough after 10 min. any idea

  • Boreeka Mar 13, 2009

    loping idle when it actually stays running start and stop actually changes type of idle until it finally warms up hard to keep idling.

  • imhighonlsb Jun 13, 2009

    it was temp sensor!!!!!!! thanx all

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Check your Temp sensor for the ecu. could be out of spec at lower temps but not enough to send a code "You know -40 is possible and won't send a code"

Posted on Nov 12, 2008

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Check those and make sure the throttle body is clean to

Posted on Nov 12, 2008

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Hj, you did not mention nothing about fuel,you should check fuel presure , fuel filter, and can add a good fuel injectors cleaner and see if this makes any difference........good luck

Posted on Nov 12, 2008

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Recently we had a GMC in the shop that at idle the RPMs would flux slightly (200-300) over idle. We put on a MAP sensor for a stored code. That did not solve it. Under closer inspection we found the EGR valve rusted out and collapsed on the base. To shorten this up it was an intake air leak. Not enough vaccume pull on the MAP sensor set the code. There are ways to find vaccume leaks. Although not the easiest. Good luck and I hpoe I helped some. Oh and check each vacume hose and pipe I beleive this car has many.

Posted on Nov 12, 2008

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