Hello there again everyone, back at it again with another issue!

I'm looking for some brainstorming help with this one.

It's a 1987 Automatic with roughly 120k miles.

I've been having a cold start idle issue for a while now. It has trouble starting in the morning: when I turn the key the starter solenoid does engage but does not spin, only after a few key cycles will it finally spin and it has to spin the flex plate a couple times to get it started(I think this is a different issue all together but worth mentioning because there is no pattern to it doing this, sometimes it'll spin right away other times I sit for 5 minutes turning the key trying to get that sweet spot) it will crank for two seconds and then fire up(sometimes longer), then it will die, then immediate start up after that. Then once it is started the idle goes up to 1300 like normal but then fluctuates back down to 800. Back up and down until it's at around 165-175 degrees. If I start it and immediately throw it into gear it either dies right away or has an extremely high idle and the vacuum booster feels like it's not working as getting the car to stop is very difficult, I really gotta pump the brakes. I have not yet smoked the vacuum lines to find a leak. It does have a slight hesitation when warm but nothing horrible like this.

I have replaced the IAC, coolant temperature sensor, the starter itself since it was due for one anyway. I'm tempted to swap over a computer from a 1988 IROC since they're the same computers, just switch proms, and see if that solves anything.

Any ideas on where to check? EGR being stuck? AIR pump stuck on? O2?

 

I would deal with the starting first. Click no start. Have battery tested. Poor connections? verify clean no corrosion / rust on battery cables where they attach to block , starter and battery. Along with connection of cables - no green or burnt red coloring of exposed wire if present. Low voltage can cause all kinds of troubles. It is possible starter is defective, some low cost rebuilts lack quality. Once you get where engine will turn over consistently I would move on to driveability. Engine does use cold start or 9th injector until engine warms up. You should verify it works.

 

I cleaned all grouns and Replaced the alternator/starter lead wire. I purchased a brand new starter, even then can still have issues but when it does start the starter sounds much better than my previous AC Delco starter. My 9th injector is deleted. I did the delete two years ago and it NEVER gave me an issue

I've been meaning to get my battery tested. I know these can be finicky when the battery is weak. Alternator charges normal. I'll test and get back.

 

Any codes? I'm sure someone with more knowledge of open/closed loop can chime in, but it appears from your post that the engine settles down when it goes into closed loop. If so, that indicates some sort of leak into the intake. (A coworker had a similar issue on a Nissan. It turned out to be a hole in his intake plenum between the MAP sensor and the throttle body) Does the brake issue go away when things warm up as well? If not, I would check for a vacuum leak on the tubing going from the booster.

 

I only get codes for burn off relay and the occasional MAF reading excessive but that one hasn't shown in a few months. And yes the braking becomes normal once the engine has settled. My intake gaskets were done not even two months ago. I'll spray some brake clean carefully and see if I get a hesitation.

 

When I lost vacuum to my brake booster, the brake pedal seemed hard and would barely stop the car. That doesn't seem like what you are seeing. Also, since it goes back to normal, it is probably not a vacuum leak there, since vacuum leaks don't tend to fix themselves.

 

That's exactly what it feels like. Very tough brake pedal and not much braking force behind it. But it does get better with warmth. I didn't suspect vacuum either. I'm pretty sure it's something electronically controlled.

I have heard of the ignition module in the distributor could cause issues like this. It was replaced with an Advance auto parts part. Most of the time they're okay but you never know how old or how many times that part has been installed

 

The hard brake pedal, to me, is a sign of a temporary loss of vacuum to the booster. The question is,"how does this happen"? This is where someone more familiar with open/closed loop can help. I'm guessing that when in open loop, you are somehow getting too much air in the intake, you lose vacuum and the car runs rough. When the engine goes into closed loop, you will get the right F/A ratio and everything runs fine.

 

That makes pretty good sense. So I should investigate fuel/air adjusting components. I did replace the O2 with an NGK a few years ago but it could still be faulty by now. My catalytic converters were plugged but have been missing since 2014 and haven't come home

It's actually funny you mention the brake booster vacuum lacking. When I dropped my car off at tire kingdom for an alignment the tech said he owned a few of these and it felt like a booster was failing, even when it's warm and settled it feels like booster. So I looked into some and they're relatively cheap and mine IS original so it can't hurt

Any input on this issue is welcome! Gets my brain working with trying to figure this out

 

The computer (ECM/PCM or whatever for your year) doesn't read the O2 sensors until it goes into closed loop. When your engine heats up, it runs better. I'm not sure if you are in closed loop by then, but if so, your O2 sensors are probably good because the F/A ratio is adjusted to where it needs to be.

If you have a vacuum gage, you can hook it to the hose going to the booster then check vacuum when the engine is cold vs hot to see if there is a significant change. Your FSM should have better brake booster diagnostics though.

 

I remember seeing that somewhere, you're right.

Well I tested my battery and it tested good just needs a recharge with 640cca and battery is rated for 810cca. That's low. I work at advance auto so I'll test it when I get to work in the am and again before I leave.

For giggles I pulled my brake booster line after driving roughly 20 minutes on my way home and had absolutely no vacuum come out with the car shut off.

 

Not sure it will hold a vacuum with the engine shut off. You should try pulling the line off the booster with the engine running. You should hear air being sucked in. If the line is cracked, you should hear a hiss when you block the end with your finger.

 

It should hold a little bit of vacuum but it will drop out after a while. This was literally 30 seconds after shut off and got zilch. I'll try plugging it the next time I drive

 

There is a vacuum check valve where the vacuum line attaches to the brake booster. I think that's preventing the vacuum from leaking off.

 

I checked that three way valve and it's good. I tested my battery this morning after driving to work and it's the same voltage. From that I can tell it's got a bad cell and will not accept higher than 640cca. I'll buy another battery and give an update!

 

Usually people have to compensate with more fuel by the ECM for that.

 

Again it never gave me problems before. What would it roughly cost to get my prom updated for no 9th injector if that really is causing me issues. I did replace the injectors with the Bosch 3 injectors from FIC.

 

It could be the conditions didn't arise because atmosphere was OK

 

So do you think a custom prom is worth getting or is the issue deeper than that? Seems odd that it would be okay for two years

 

Do you have any other mods? How willing are you to live with this? For me, I would get the CSI cleaned and replaced or if I have enough mods like intakes, headers, etc, etc, get someone to burn a custom prom either by mail or dyno. So when I got intakes, headers and an exhaust on my F-body, I brought it to Lingenfelter and had him do it. Also, I wanted to meet the guy personally. I can get it burned by Hitech Motorsport in MN via mail order but it would never be as close as a dyno tune. If you are willing to live with that, it is about $275.

Regardless, now that you have changed the parameters, it is unpredictable so if you are getting a custom burn via mail order, I'd ask Jon what the flow is at 43.5 psi, tell that and the other mods to Bart at Hitech and have them burn something. That or dyno tune.