Why does my Bonneville not idle by itself then sometimes works great?

jhaase3

So it willit will be running fine And when I hit the brakes it will die once the rpm Get to 1 . If I keep the gas on And don't let it get to low it will stay running. it will do that for a while And then work fine.  Some days it won't idle when you first start it But as long as you manually keep it going it will. I changed the throttle position sensor,crankshaft sensor,wires,plugs,battery anxious alternator are Good. I am at a loss. it has 246000 on it. 

imidazol97

jhaase3 said:

So it willit will be running fine And when I hit the brakes it will die once the rpm Get to 1 . If I keep the gas on And don't let it get to low it will stay running. it will do that for a while And then work fine.  Some days it won't idle when you first start it But as long as you manually keep it going it will. I changed the throttle position sensor,crankshaft sensor,wires,plugs,battery anxious alternator are Good. I am at a loss. it has 246000 on it. 

Do you know what year your Bonneville is? Is it supercharged or the normal engine? Are there any pending codes showing on a scan of the computer? You didn't mention the engine light coming on so I suspect you haven't had it scanned. I'd suggest that.

Has the upper intake "plastic" manifold been replaced? I have read
of vacuum leaks around the bottom seal with age. That changes with
temperature so it gives odd symptoms. With engine idling you can
spray carb cleaner around the edges and around hoses to see if you've
got a vacuum leak sucking in air.

Has the throttle body been cleaned to remove the gunk
that builds up around the butterfly plate which can affect the idle?

Has the IAC (idle air control) been cleaned? Do not dip it but it may
have carbon around it, both in the opening it sits in and on the pintle
of the valve.

Has the MAF been cleaned with a liquid spray to clean the dirt bits
that can end up on the two wires that measure the air flow rate?
The backyard check for the MAF is disconnecting it and seeing if the
problem goes away.

jhaase3

It's a 98 And Yeah the check engine light comes on for a while And then it will just shut off. The car will not stay running with it on or off. And then some times It's fine. I have cleaned the maf sensor And throttle body. And put a new throttle position sensor. My light has been off for a week And when I scanned it,the throttle position sensor And both o2 sensors. They have all been replaced And everything cleared And still the same thing. I have also change d the pcv valve. 

imidazol97

jhaase3 said:

And when I scanned it,the throttle position sensor And both o2 sensors. ;

Your sentence has some words missing. What did you get when you scanned the computer?

First, you've replaced several parts and they may not have been needed. Also,
the oxygen sensors that are off brand replacements sometimes are trouble them-
selves even though they are new. Only one of those sensors actually is needed;
the other one just serves as a check.

When the engine will not stay running, does it always start back up? If it doesn't,
you need to have removed a plug wire so it's easy to slip off again, put in an old
spark plug and lay it on metal of the engine. Have someone crank while you watch
for the spark you're getting across that plug. They also sell spark plug gadgets
that you can put on the wire to show a gap and let you check the spark color and
strength. If you're getting no spark while the engine will not restart, then crankshaft
position sensors wear out and the spark control module under the coils can also
give trouble, especially when hot.

If you've got spark then you may not be getting fuel.

Something to try is to remove the connector from the MAF and see if that
changes this problem. It may not be the MAF, but at least it's a place to
start.

Beyond that you need someone with a scanner that's able to look at the
mixture counts that the computer is using to go rich or lean and see what
is happening at a higher level of analysis.

Good luck. But you may need to have a good dealer analyze the problem
or a good shop that actually has the technology and the SKILL to analyze
what's going on.

jhaase3

Yes it restarts everytime. But I will have to keep it running with the throttle or it will die. I'll use 2 feet while I drive And then I'll see if it dies. Sometimes it will Stay running And sometimes it won't. I have changed the crankshaft sensor about 2 months ago. 

imidazol97

What happened when you unplugged the MAF and ran it?

jhaase3

See I just unplugged it while it was idling. Nothing changed on it then.   do I need to unplug it And drive it like that? 

imidazol97

IIRC you can drive it that way. It may be in a limp mode and may set the check engine light. But that
will go off when you plug MAF back in. Do you have a friend with the same or similar car with which
you can exchange the MAF to see if the other known good MAF fixes your car's bad running?

I will do some reading a Bonneville forums to see what I can learn. If you should get a replacement
that you buy, get a good brand. I see rockauto.com has AC Delco for $171 plus shipping. There is a 5% discount number available on the internet that might save enough top pay the shipping. A Dorman
runs about $80.

imidazol97

jhaase3 said:

I have also change d the pcv valve. 

Did you put the o-ring on the outside of the PCV?

Another thing to try for the idle problem is to unplug the MAP sensor. It's on top of the PCV housing.
If you unplug it an the problem goes away....