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Matt, Engineer
Category: Pontiac
Satisfied Customers: 21864
Experience:  Honors degree in Mechanical Engineering, worked 8 years as a Formula 1 engine engineer.
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I have a restored 1984 Pontiac Fiero w/ 2.5L engine (rebuilt

Customer Question

Hi! I have a restored 1984 Pontiac Fiero w/ 2.5L engine (rebuilt from 86' Fiero donor). On cold startup, high idle - 3,000 RPM's. After she warms up a bit, idle drops to 1,500 RPM's or so but is erratic (drops to 1,000 then back to 1,500). Engine is also misfiring. Have checked for vacuum leaks - no luck. All new sensors - PCV, IAC, TPS, EGR and gaskets. Please help! Don't know what else to do!
Thank you,
Owings Mills, Maryland
Submitted: 10 months ago.
Category: Pontiac
Customer: replied 10 months ago.
I forgot to mention - ECM w/ PROM was replaced too (from 86' Fiero 2.5L donor).
Expert:  Matt replied 10 months ago.


In that case I'd suggest to 1st remove the intake and ensure that the throttle blade is clean and free from dirt that would prevent it from fully closing

and the best method for checking for a vacuum leak is to have the engine running and warm and then spray lighter gas /propane or brake cleaner around each joint in turn. If the engine rev's up you've found your leak.

Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.

Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.

its also worth disconnecting the brake servo hose and plugging it on the engine side

as I've known brake servo's to leak and allow air into the engine that way