Long time lurker first time poster. Thank you to anyone who has ever posted their information to this forum. I have used this forum many of times to help reslove many issues on my 84 2.5l 4 speed and to decide what parts to buy and where to buy them.

Shortly after I purchased my Fiero I started having engine troubles. I end up having the engine rebuilt by a very respected engine shop here in Indianapolis. When I finished installing the engine it was nearly summer. I did not have any idle issues the engine ran fine. Now that it is getting colder here in Indy the cold idle is getting rougher the colder it gets. Once the car warms up, the idle is smooth and steady at 950 rpm. I'm getting 25.5 to 26.7 mpg in country/city driving. WINALDL shows no set flags, engine temp to the ECM matched the outside air temp at start up and increased along with the dash guage to 181 degrees and remains constant. As far as I can tell all values that can be read through WINAlDL are witin limits. All engine sensors have been replaced along with EGR valve and IAC. All vacuum lines and fittings have been replaced. New battery and alternator. I think i have replaced everything in and on the engine.

I found a post by "Perceptionist" dated 10-08-2009 reguarding his problems with rough idle.

https://www.fiero.nl/forum/Forum2/HTML/103899.html

Like Perceptionist as one of the troubleshooting steps I tried before I had the engine rebuilt was to take apart and clean the TB. ( I did not mess with the idle set screw ) He posted a picture showing the various holes in the IAC circuit. I understand whitch holes he is refering to and where they are in the TB. However he discovered that the "#3 hole" was blocked by the gasket that went between the TB halves. He stated that he cut the gasket that was blocking the #3 hole IAC passage.

My questions are: Where did he cut the gasket that goes between the halves of the TB to clear the #3 IAC passage? Is there a picture of what the TB gasket should look like for a 84 Duke?

Thank you in advance.

The IAC controls the amount of air that flows into the intake at idle. The passage allows air to flow around the throttle plate when closed. I doubt your IAC passage is blocked since your idle when warm is fine. You can check to see if your IAC passage is open by warming up the engine, then unplugging the IAC, and then removing the IAC. Now start the engine and see if you have a very fast idle. Stick your finger into the IAC hole and partially plug the passage and see if you can control the idle speed. If you have no vacuum at the IAC hole and your idle didn't jump after removing it then you should look for a blocked passage. If however the idle jumped, and you can control the idle speed with the hole then your passage is open.

I would think you have checked these already but have you looked at your plugs? Preformed a compression test??

Welcome to this big family. It seems your problem is only in open loop, as soon as your 02 warms up it runs fine. And as it gets colder it'll get worse.. Another fellow that had an 88 duke also had the same problem and every time the car cool down for a couple of minutes and started right back up it would hardly idle, as soon as the car got in close loop it ran as smooth as silk. I fixed that problem in my car by installing a 4 wire 02. Open the ignition for 5-15 seconds depending on the weather outside before starting the car. It cuts the time the engine goes in close loop by a substantial margin. Want to wire one? Do a search here and you'll find how. Hope this help.

quote Originally posted by A Woodward: Long time lurker first time poster. Thank you to anyone who has ever posted their information to this forum. I have used this forum many of times to help reslove many issues on my 84 2.5l 4 speed and to decide what parts to buy and where to buy them. Shortly after I purchased my Fiero I started having engine troubles. I end up having the engine rebuilt by a very respected engine shop here in Indianapolis. When I finished installing the engine it was nearly summer. I did not have any idle issues the engine ran fine. Now that it is getting colder here in Indy the cold idle is getting rougher the colder it gets. Once the car warms up, the idle is smooth and steady at 950 rpm. I'm getting 25.5 to 26.7 mpg in country/city driving. WINALDL shows no set flags, engine temp to the ECM matched the outside air temp at start up and increased along with the dash guage to 181 degrees and remains constant. As far as I can tell all values that can be read through WINAlDL are witin limits. All engine sensors have been replaced along with EGR valve and IAC. All vacuum lines and fittings have been replaced. New battery and alternator. I think i have replaced everything in and on the engine. I found a post by "Perceptionist" dated 10-08-2009 reguarding his problems with rough idle. https://www.fiero.nl/forum/Forum2/HTML/103899.html Like Perceptionist as one of the troubleshooting steps I tried before I had the engine rebuilt was to take apart and clean the TB. ( I did not mess with the idle set screw ) He posted a picture showing the various holes in the IAC circuit. I understand whitch holes he is refering to and where they are in the TB. However he discovered that the "#3 hole" was blocked by the gasket that went between the TB halves. He stated that he cut the gasket that was blocking the #3 hole IAC passage. My questions are: Where did he cut the gasket that goes between the halves of the TB to clear the #3 IAC passage? Is there a picture of what the TB gasket should look like for a 84 Duke? Thank you in advance.

You won't have the same kind of problem, since there is no gasket- you have a different style of throttle body.

Start with checking your fuel pressure. There's a fuel pressure kit you can rent from Autozone for a $150 deposit. If you have single-digit fuel pressure, your cold starting will be weak and rough.

Thank you for the replies.

I have to wait untill this weekend, but I will start with warming up the engine and removing the IAC to see if I can vary the Idle speed.