A couple of weeks ago I bought a 85 4+3 coup. Now that I've had a little time to drive it, I've noticed a few annoying problems. If anyone has some insight into how to fix these problems, I would appreciate the help.

The most annoying thing is the rolling idle. When the engine is warm, at stop lights, the engine idle will pulse between 400 and 800 rpm. It will do this endlessly. Twice it has just died. If I use the accelerator pedal to bring it up a bit (say 1000 rpm) its steady, but will return back to rolling idle if the pedal is released. The only way I have found to stop this is to turnoff the ignition and restart. Then it idles just fine at around 700 rpm. WTF?

Problem #2: Cold start is never easy. I haven't yet found a scheme to get the engine started the first cranking. The closest I've come is to slowly depress the gas pedal while cranking which may or may not ignite the engine the first try.

Problem#3: When the engine is warm, and I shut down for more than a couple of minutes, it's hard to start and a big puff of pure gas fumes exit the exhaust. Gags everyone around.

Are all these problems related? What component(s) should I be looking at?

Thanks for your help.

 

# 3 sounds like an injector is stuck open, and the rest sound very fuel related - fuel pump, relay, fuel pressure regulator. You definitely need a shop manual from helms to help diagnose. Could be TPS, idle air control, or a conmbination. Try cleaning the throttle body if you haven't done so. Not to insult your intelligence, but don't step on the gas to start her up - FI cars don't need that. HTH

 

I got a 85 4+3 and it did the same thing, run rough idle up and down, after a long battle with it, I found two injector's leaking, replaced all eight and now run's great. This was my cure, Hope you find yours.

 

Thanks for your help. I know I should not have to touch the gas to start FI equipped vehicles, but it won't start if I don't

 

I'll try this first, thanks

 

If you can live without your car for a week or two, you can get your injectors serviced by CruzinPerformance.com. Rich does nice work and it is a lot cheaper than buying a set of injectors. It definitely fixed my warm start problem, and smoothed out my idle as well.

Pulling the injectors on an L98 is relatively involved, but it will give you a chance to clean the throttle body/plenum if you do it.

 

I probably would go along with this suggestion also.

I had the same problems 4 years ago. I just ran a bottle of injector cleaner through it, and it cleared up most of the problems. I still have minor (~100rpm) flucuations at idle when warm - 900 down to 750 then back up to 900 again, but no cold or hot starting problems.

Keep searching, and good luck.
Finding the problems and the cure are quite satisfying.

 

I put a bottle of Berryman's Injector cleaner in last night when I filled up the tank. We'll see what happens. Thanks all for the feedback.

 

Don't start throwing $$$ at it without doing some testing. Do you have a digital volt/ohm meter? Check the ohms across the two spade terminals on your injectors, I believe the number you want to see is around 16 ohms, if this is wrong someone please tell him different. Mainly they should all be close to the same reading. Do you have a fuel pressure gauge? Hook it to the schrader valve, start the car and note the pressure, then shut it off, if you have injectors leaking the pressure will drop right away, if not it will hold for a spell before slowly dropping. Narrow things down bit by bit until you get it. Believe me, I have been through he11 with mine but thanks to the guys on this forum and a lot of cussing and testing my car now runs like a champ.

 

OK Midnight, the VOM I've got and I can probably find a pressure gauge. When the weather gets a little better around here, I'll try your approach.

 

Well, the Berryman's made a big difference in the rolling idle problem. Now instesd of 400->900->400 rpm, it's 650->700

I still have hard starting problems though. I'll try a new cold start valve this week and be prepared to do more with injectors later if problems return.

Thanks for your help.

 

Great!
Sometimes a complicated problem has a simpe solution.
Sure does lend credence to the point made above about plugged injectors.

 

Before you buy a new cold start valve, check it out too. Take the connector off the valve, then use your tester light to determine which terminal is the hot one. You will have to crank the engine to get the light to come on. Once you find the hot terminal take a jumper wire and put it between the corresponding spade on the valve and the hot terminal in the connector. Then ground the other spade in the valve, try to start the car, if it fires right up then your problem is the cold start sender which is located in the front of your intake manifold. It is the larger of the two that are right there side by side and it has the same style connector as the injectors do. This is a pricy little item at over $80 dollars at GM and NAPA both. I got a used one from Jay at Vette2Vette and it worked great, I have no more cold start problems. If you need further coaching just email or pm me and I'll see what I can do.

 

You already have some great advice from the previous posts. I will add that the hard warm/hot start problem is usually leaking injectors. If that is the case and you can't get it fixed right away, holding the throttle wide open while attempting to start will help with the warm/hot start condition.

What happens with a leaking injector(s) is that the fuel rail holds pressure even while the key is off. The leaking injectors will drip fuel into the intake port and essentially flood the engine. If you hold the throttle wide open while trying to start, the air rushing in helps to evaporate some of the fuel and allows the fuel/air mixture to ignite.

Sorry so winded.

Mike.

 

Just wondering if you've found your problem yet.

 

Thanks Midnight for the advice. I haven't got to the starting problem yet. I got side tracked with a few other electrical things, but I will try what you described.