Chevy & GMC Vans

got to love new projects:). i have acquired a rough idle. but it only idles rough at a stop light or stop sign. it started after i changed the air filter and pcv valve. is the a simple solution to fix this? ty for any tips or suggestions. this is in my 1990 astro van.

check for leaks in your intake and vacuum system.

Also pull and check the EGR for carbon deposits.

LiftedAWDAstro wrote:Also pull and check the EGR for carbon deposits.

that's got my vote (depending on how rough)

what is the EGR? still learning terms also.

Exhaust Gas. Recirculation


I allows a bit of your exhaust to go back into the intake to burn off some of the extras that get through the first burn.>> ( i think.... could be wrong....Been a while since i splained this stuff)

Its part of the emissions system..

Should be able to trace it as a pipe that comes off the exhaust manifold an goes over to the intake manifold. There is a valve in there that regulates how much gets back in based on the sensors in the exhaust.

My take on EGR a little different.Using hot detonation prone air lacking oxegen from its first trip through the cylinders.To try to burn gas.Causing that fuel to misfire causing worse emissions and robbing power.Maybe I wrong but I never heard any goverment agency ever claim carbon monoxide and hydrocarbons would burn gasoline.I just dont know how good the LSD was when they thought that was a good idea.Surely the first engine with it was a clue.They eventually did away with them on most engines.Think it was the poor mileage and emissions?Okay I a smart aleck.But these facts are so obvious a blind man can see them.

EGR lowers the combustion temperature to reduce NOx emissions. Excessive EGR can cause misfires and partial burns, but properly tuned, it can improve efficiency.

NOX emissions actually are from improper air fuel mixture.To lean.I got mine blocked better milage and alot more power not seeing downside.

Try searching through any EGR posts to see if you can find a pic of where it is and what it looks like. I will do the same.

EDIT: found some pics.

These are of Lockdoc's 93. Not sure if your 90 is in the same location or not.



See the little chunk in the hole?



Here it is!

this to a 90 van my 94 electronically controlled.On tbi it behind Injector unit On w motors it under the plastic intake.There are two openings on one pictured had to have center hole to work.On my 94 just a flat plate with th bolt holes.I can dig up a picture of w Motor placement

chevymaher wrote:NOX emissions actually are from improper air fuel mixture.To lean.

Precisely. The exhaust gas displaces oxygen making the mixture richer, and lowering combustion temperature. Nitrous Oxides form when Nitrogen and Oxygen from the air combine at high temperatures. Unsophisticated 1970's EGR systems had side effects, but modern EGR systems improve performance and economy without affecting drivability.
A malfunctioning EGR will trigger the trouble light, and you may not pass emissions testing.

This my spare motor it in the back of intake between intake and distributer.My 94 has same EGR valve as you show on that CPI motor But on TBI it located in rear as 90 motor shown

timelessbeing wrote:

chevymaher wrote:NOX emissions actually are from improper air fuel mixture.To lean.

Precisely. The exhaust gas displaces oxygen making the mixture richer, and lowering combustion temperature. Nitrous Oxides form when Nitrogen and Oxygen from the air combine at high temperatures. Unsophisticated 1970's EGR systems had side effects, but modern EGR systems improve performance and economy without affecting drivability.
A malfunctioning EGR will trigger the trouble light, and you may not pass emissions testing.

I dont have emissions testing,and I got older garbage style.I will go with delete and setting air fuel mixture correctly.Getting rid of hot intake air and adding more oxegen a power adder.More fuel and more air more power. And 800 degree air is not good for combustion.They may have improved it but it better without, if again the key is tuned correctly

EGR is supposed to improve combustion as well. It's not as simple as more air=more power.
There's other effects to consider like:
Reduced throttling losses.
Reduced heat rejection.
Reduced chemical dissociation.