Hi, I just bought a '89 IROC convertible that needs quite a bit of work. First off, I think there's an issue with the IAC because the idle speed fluctuates between near stall and high revs. I'd like to take it out and maybe try cleaning it but I don't know what size socket it takes or if that would help at all.
The tach itself doesn't seem to be working right either. On ignition, it goes right to 3500 rpm but seems to work somewhat after that (using 3500 as 0 rpm). What can I do to fix this? It's the stock gauge cluster and I'd like to keep as much stock on the car as I can, including the tach.
Also, I just installed a radiator and it works great. However, the temp gauge doesn't work and the cooling system is always running full capacity with both fans going. Is that really a big deal? What can be done to get my temp gauge to work?
I have plenty more things I need to fix on this car and this is just a start for me. I'm new to the game and would greatly appreciate all the help and advice I can get. Thanks.
Tyler

 

It sounds like someone yanked the instrument cluster out without disconnecting the battery, fries the tach about 50% of the time. Unhook your battery, remove the instrument cluster, check the circuit board for damage, reinstall the cluster and bolt it in using the 2 bolts on the bottom (in the lamp holes), hook up the battery and see if you have the same problems. If so, get a Chiltons book (with diagrams), a good quality ohm-meter and start tracing!

 

Tach reading high is caused by a degradation of the capcitors. You can replace them. Search for "tach capacitor" and you shuold find what you need to know.

 

Hey guys, thanks a lot. I will hopefully be able to go take a look at it tomorrow and see what I can accomplish now that you've given me some food for thought. Do you have any advice what I should do about my IAC issue? I'm beginning to wonder if some of my problems i.e. the CTS, oil pressure gauge, tach aren't all related. Hopefully I'll be able to figure it all out soon. Thanks a lot though!

 

go to this sites home page go into tech aritcles and read about IAC/TPS adjsutments. also can be found in a chiltons repair manual and other repair manuals for your car

 

You can easily disconnect the CTS (front of the engine, under TB) and measure its resistance. It should read around 1 or 2 KOhms with warm engine. I can post exact temp/resistance tables later.

Did somebody try to tune the car before? Because if the memcal is not inserted properly all the way, the car will run in limp mode, with both fans running the moment you turn the key etc.

Lou

 

memcal? my single fan is on as soon as i turn on the ignition always has been since i bought the car 8 months ago. i have a 305 tpi v8 5.0 automatic trans am. could my car be in limp mode and what can i test or replace to find out?

i just figured the guy shorted the fan so it would be on all the time becuase the car had over heating problems at one time

 

If it's only one fan that's constantly on, then it's not in limp mode. I misinterpreted your sentence "with both fans going".

But you can test the CTS (as I posted before) and also the gauge temp sensor (in the driver side head, between first and second spark plug), with the green wire.

Hope this helps.
Lou

 

Wow, more comments! Okay, I'll admit, I am still very new to this....what exactly is memcal? I don't know a whole lot about the car history but know that it was his everyday driver turn project car that sat a couple years and he just never finished. I didn't get over to look at my car today but hopefully on Thursday. I'll do what you've suggested. Thanks!

 

A "memcal" is a memory calibration module that resides in the ECM case and sets the engine parameters. If it's missing, the ECM will run on some basic generic parameters so that you can get home but the engine won't run good. But at least it will run and you can "limp" home. Which explains why they say that the engine is in "limp mode".

Don't worry about the memcal, it was a diagnose mistake on my side. Yours should be ok.

Lou