Revving up and down when just started

buick
lesabre

#1

All,



My 93 Buick LeSabre has been having an issue every time I turn the engine on. This is especially true if it’s colder out, like in the morning. When I just turn it on, it will sound normal for about 10 seconds, but then rev up pretty high, come back down below the normal level after 2-3 seconds, and quite often even die right there, at the bottom level, unless I give it a little gas. It will do this up and down revving about 5-8 times until it stabilizes and idles somewhere in the middle.

And the funny thing about giving it gas, is that instead of revving the engine, it feels like it’s closing a valve somewhere. When I press the gas lightly, the engine goes from normal sounding to almost silent. Seems like the exact opposite of what the gas pedal should do. However, if I almost floor it, then it will sometimes break through and be fine.



This only happens when I start the car. First, I assumed that it was only when the engine was cold, but I can drive it for a while, then stop somewhere for 5-10 minutes, come back, start it up, and it will sputter very briefly, maybe 10 seconds, and be okay.



Does this ring any bells for anyone?



It’s been this way for almost 2 years now, and I’ve learned to live with it, but would really like to see if it’s something that can be easily identified and hopefully fixed.



Many thanks!


#2

What maintiance has this car seen in the two year period that the idle has been a problem?

Do you have a manual for this car? many contain flow charts that help resolve these type of problems.


#3

It’s had the problem from the day I bought it, so I’m not sure if it’s a problem with maintenance during the past two years, but I do regular maintenance on it - oil change, spark plugs, air filter, etc.

The manual that I have is more a general info about the car, no flow charts there.

Could this be a problem with PCV valve? EGR valve? Idle control sensor?


#4

Sounds like a wicked vacuum leak from somewhere.


#5

Surging and bogging down when you open the throttle means the engine is running lean. It doesn’t turn the engine light on because the oxygen sensors haven’t warmed up yet, so the computer doesn’t detect the lean condition. This car is OBD1 I think, so the computer diagnostics are not very sophisticated anyway.

It could be a bad coolant or intake air temp sensor or MAF sensor. The engine computer has to estimate the amount of gas to feed the engine before the O2 sensor warms up. Once warmed up the O2 sensor sends a signal to the computer to pick the correct air/fuel mix.