Just got back in from spending almost ten hours putting my car back together (this is the '89 IROC in my sig). This is the second time that I've had to completely re-assemble my engine since a rebuild that started a year ago (some of you might remember me ).

Anyway, the subject mostly tells the story. I just fired the car up, and after playing with the distributor a bit, I got it to start. After it started, I treated it as if it was a rebuilt engine being started for the first time--I didn't let the engine speed drop below 2000 RPM, and I varied it up and down from there (don't know if that was necessary or not). Once I was done doing that, I let my foot off of the gas. Felt like it wanted to die, so I changed the timing a bit. I eventually got it to idle on its own--but it was "idling" at 1500 RPM.

One thing I did notice, by the way, was that the throttle response was *very* sensitive. Mabye it's because I'm not used to a V8 car (I've never really been able to drive this one), but I could barely touch the gas and the engine speed would jump 1000 RPM very quickly.

So it's sitting and idling at 1500 RPM, and I then tried to put it into gear. When I did that, the engine speed dropped dramatically and it wanted to die, so I put it back into neutral; engine speed shoots back up to 1500 RPM. When it was in gear, it didn't even feel like it wanted to take off. So I let my dad get in, and he managed to keep the engine running while in gear, but it sounded extremely rough. He pulled the car out and made a circle around the cul-de-sac and pulled it back into the driveway. He was somewhat deep into the throtte just to keep the engine running. I also noticed from outside that the engine was backfiring through the intake.

Any ideas what my problem could be?

 

I would suspect a large vacum leak. Check around the intake and check to make sure you hooked all the vacum lines.

 

If it's a vacuum leak, then my next question would be how to find out (not even where the leak is--just weather-or-not I have one). I do have a vacuum tester gague, but remember that the idle is very high. Wouldn't that higher idle speed throw my vacuum numbers off dramatically.

Also, how much vacuum should I be expecting at a normal idle?

Thanks

 

I believe normal vacuum should be 17 to 22 if you still have the stock cam. You can inspect all your vacuum lines and make sure they are all hooked up. Then you can spray some carb cleaner aroud the intake and throttle body area while the car is running and listen for the idle to change. Be careful around the distributer since carb clean is flammable. I would also try to retard the timming some, as that can also cause a backfire and high idle.

 

My similar problem for this condition was valve adjustment.

It could be lean mixture or vac leak as previous said.

Check for vacuum at oil dipstick tube too (probable bad intake manifold gasket or bad int. manif./headers matching or cracked int. manif.).

How is the coolant temperature?.

 

Thanks for all of the replies.

I *finally* figured out what it was: <i>bad ECM</i>. Popped a new one in, and that fixed nearly ten different problems that have been plaguing me for a year. (i.e. it can sustain an idle, it can stay in gear, doesn't blow black smoke out of the tailpipes, the fans aren't both always on, the SES light doesn't flicker, and the list goes on...).

I think I'm going to put a post up to remind people who are having impossible-to-diagnose problems with their cars to make sure the ECM is working. I probably have more than fifty printed pages of correspondence on these boards over the past year with people trying to help me and me posting back results of tests. I even pulled out this engine and tore it down for a second time just to chase this problem. And all this time it was the ECM...


Denis. V: Interesting you bring that up... I definatly need to adjust my valves. At least one is clanging very loudly--I can hear it from inside the car! Also, the coolant temperature (the gague on my dash) is very high--it peaks at the line that's above 220 but just below the beginning of the redline (these gagues are sometimes hard to give a numerical value for). I would imagine that's partially due to the fact that this is a new engine and it's supposed to run hotter--but hopefully it will go much lower once I have all of the valves adjusted properly. Also, my computer thinks I have a bad MAF sensor, so that could be altering the air/fuel mixture, in turn adding more heat.