lead ignitor?
 

lately i have been having a problem while driving and such where my exhaust overheat light comes on and my idle drops to about 650 rpm or even 500 or lower at times, and the car shakes really bad. sometimes it lasts a long time before the light goes off and the car idles normally again and sometimes it does it right after i start the car. when the light is not on the car idles smooth as silk at 750-800 rpm and doesnt smell rich, and while driving when the light comes on i lose a little power.

im assuming that the exhaust overheat light is coming on because my cat is getting hot (duh) and if the ignitor is going and a rotor is not working properly then the mixture would become rich and that would heat up the cat right? i am also assuming that it is the leading ingnitor because the tach doesnt jump or anything when the light comes on it just drops to a lower than normal point on the tac and if i give it a little fuel the tach responds beautifully.

what are other things to look for in means to resolve this issue? i have checked for vacuum leaks and have not been able to locate any and i have replaced all vac hoses under the hood that i found. any help would be appreciated.

oh yeah this is on the 82 12a

if your tach is acting up then the ignitor is going. well thats what happened to mine 100 miles before it went out.

F.Y.I
rotornoob is refering to Lead Ignitor.
The Tach is hooked up to the Trail Ignitor and Coil!
Did you replace the Hose above the Exhaust Manifold?
I believe it's the Hose that goes to the Port Air Switching Manifold.
This hose tends to go bad because of the heat. It will play havick with your Idle System since you indicated that heat seems to be playing a role with your problem.
Just a thought!

If you have downloaded the FSM look on Page # 4A-26. This will show you how to do a check on the Heat Hazard System.
The following pages will also give you an idea what to check in some other areas that have to do with what problems you seem to be having.
I'm leaning towards Emission Problems since you stated your motor is stock and the Rat's Nest is still intact. Chapter 4A will help you through most of it. Also it includes the Cat System.
sgieldon
steve

thx steve i will check that after work tonight. i did replace that hose/tube above the mani so i will spend time with the FSM. just in case, i went to pick and pull and got not one but two ignitors for free ( 5 fingered them ) and they seem to be in decent repair, and i even found a nice bonus i hope to install soon...an e-fan from an 85 mr2 :)

if anyone in my area needs parts there are 2 second gens and 3 first gens there right now mostly intact. this was at the stockton pick and pull. also there were a few more mr2s there for those that still need electric fans and such. i only payed 30 for mine

Check on that lead ignitor. Just pull the plug wire off one of the lower plugs, and stick an old (if available) plug into it. Set the plug on the strut tower and crank her over while watching for spark.

If the lead goes out, then the fuel will ignite later in the cycle. There will be less time for the flame/heat to dissipate, which means more heat for the exhaust system. So based on the information available to you, it sounds like you were on the right track. :)