Chevy Astro and GMC Safari Forum banner

Wants to stall when shifting from Drive to Park

3K views 14 replies 5 participants last post by  nu85 
#1 ·
Ok, this is driving me nuts. For the past couple weekends I've tried to find out what is making this thing idle like a pig. Replaced the cap and rotor, plugs and wires, all vacuum lines, replaced the IAC, Took off the EGR valve, cleaned and installed a screened gasket, checked for a vac leak around the intake.

Here is the issue... First start in the morning- one crank and its runnin, idles pretty high for a second then drops down. Drop it into Drive and the idle goes way up for a second and then falls back down again.

Engine at operating temp... come up to a stop and everything feels and sounds normal, but as soon as I come to a stop I get a rough idle. If I go from Drive to Neutral or Park it will stumble and sometimes die and sometimes it will catch itself and idle.

Now I get a Service Engine Light. Im getting a PO420 - Catalyst System Low Efficiency. :banghead:

Wave your magic wands and tell me what to do next!
 
#2 ·
Are you SURE you've ruled out a vacuum problem? If so, I'd be looking at the 02 sensor and the MAP/MAF sensor. It seems to me that the engine's not able to follow the load quickly enough.

Take a close look at what happens when:
  • shift Drive to Neutral[/*]
  • Shift Neutral to Park[/*]
  • Shift Neutral to Drive[/*]
  • Shift Neutral to Reverse[/*]
  • Shift Reverse to Neutral[/*]
  • When the transmission shifts automatically from 2nd to 3rd (about 28mpg)[/*]
Pay attention to the RPM, is it going up or down. There are different transmission clutches involved that put a different load on the engine.
 
#3 ·
LEVE,

No, I havent ruled anything out. but I dont know what else to check. I thought of the O2 sensors and/or the Cat when I saw the code it gave me. But then it's kinda vague, PO420 - Catalyst System Low Efficiency

It was running rich... er...ish until I changed the vacuum lines, so figured I had it.... out of the way. Could that have done something to the cat and/or sensors and cause it show those symptoms? it never threw a code before, then I started replacing everything. But no, I havent ruled anything out.

Drive to Neutral... rpm's will dive and want to die. sometimes it catches itself and recovers enough to idle, and the idle is rough.
Neutral to Park... not much of a change, its either idling rough or sometimes (very rarely) will idle like its supposed to.
Neutral to Drive... idles up and wants to take off, then backs right down to an idle. sometimes it will idle right, most of the time not.
Neutral to Reverse.... same procedure.
Reverse to Neutral... not much of a change again.

I have tried going through down shifting to see if it effected what happend when it came to a stop, not really. Still a rough idle.
I tried... when rolling up to a stop, shift it into neutral and then come to a stop, shift it back into drive.... rough idle.

No tach, but I can watch the oil pressure gauge dive and rise, so know the engine is stumbling.

:banghead: :banghead:

Thanks !!
 
#5 ·
LEVE,

On a cold start, it cranks all the time, every time on the first turn. Idle is a little high, but smooth. A few seconds and it will drop down a little but still idles smooth. As soon as I shift into what ever gear, it idles up for a second then drops back down again and is a little rough.

Love these vans but sure hate the engines nowadays. It this were my ole Impala or Willys, I could figure it out, but with all the dang spaghetti of vacuum lines, wiring and sensors its like looking inside a computer! Guess Im showing my age. Now I know how Pops felt when he couldn't program their VCR!
 
#7 ·
Well I just started hearing the cat rattle yesterday. Pulled into an alley and had the passenger side window open and as Idled down it I could hear the rocks in a tin can. So I am guessing that it whats making this thing idle rough. Would it be wise to replace the 02 sensors also?
 
#9 ·
The guy I bought it from kept immaculate service records, I went through all of them and didnt see any work done on the exhaust, so i am "assuming" the 02 sensors are original. I'm 12V electrically challenged, confuses the hell outa me. 110V, 220 AC, not a problem dont ask me why, i cant figure it out either. So... how do I go about checking its voltage. Is there a PDF somewhere I can follow?

Thanks guys, was getting to the end of my rope with this thing! :evil:
 
#11 ·
Nope. It "runs" like a champ, no hesitation, missing, bogging or anything. It just doesnt idle worth a damn.

Side note: Stopped by the muffler shop yesterday just to see how much it would cost me to get the Cat replaced. Well dude says "did you hear California's new law on these?" I cant order a Cat online and have someone put it in anymore. Then they upped the stupidity... every vehicle (like all 1999 Astros) have a specific number for the Cat. Now this guy said if I dont use a Cat with that number it wont pass a smog check. I have never had any one crawl under and check the Cat at a smog test, so I dont know how they would know if it wasent the right Cat California wants. And of course the Cat is $300.00. See what happens when you have a bunch of left wing, tree huggin, 60's hippies in power in California. They didnt have much sense in the 60's, and it didnt improved much as they got older.
 
#13 ·
Woodweasel said:
It "runs" like a champ, no hesitation, missing, bogging or anything. It just doesnt idle worth a damn.
Woodweasel said:
It this were my ole Impala or Willys, I could figure it out,
Forget about all the electronics for a moment and find out if the engine is running rich or lean at idle. This may require a helper in the drivers' seat. Add propane for lean or pull the PCV valve hose and meter with your thumb for rich. Which one makes the idle smooth?
 
#14 ·
#15 ·
"See what happens when you have a bunch of left wing, tree huggin, 60's hippies in power in California. They didnt have much sense in the 60's, and it didnt improved much as they got older."

:rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: TRUE

Actually....some smog shops look underneath to check out cat. They can tell just at a glance as aftermarkets look distinctly different.
However, you can slip $125. - $250 to MOST smog shops and get passed. When I owned my smog shop 20 yrs ago it was more rare to find an illegal shop, yet now that they have changed rules to toughen the ability for an illegal smog, many shops do it. It is a racket in Cal. Go get your smog test and fail nox, the shop will say "replace cat"....go to abc shop and get it" abc shop being this guys brother or cousin. Yes, a new cat will reduce emissions accross the board and allow almost any car to pass but nox can be other things too.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top