chugging on start

the car is running fine but every so often when start the car the engine chugs for about 20 second or so until idle catches and everything is fine again, it only happens when I do a lot running around (parking run in store go to the next ect ..and only when the engine is warmed up, my mechanic did change some of the fuel lines, fuel filter was done at tune up.and it might happen once every 2 weeks,cam sensor also,pcv,any suggestions to keep an eye on are welcome,thanks for reading stay safe in healthy

My car does that too. I was hoping it would get fixed when I send out my PCM for a tune.

Rivieraz wrote:

the car is running fine but every so often when start the car the engine chugs for about 20 second or so until idle catches and everything is fine again, it only happens when I do a lot running around (parking run in store go to the next ect ..and only when the engine is warmed up, my mechanic did change some of the fuel lines, fuel filter was done at tune up.and it might happen once every 2 weeks,cam sensor also,pcv,any suggestions to keep an eye on are welcome,thanks for reading stay safe in healthy

When was the last time you removed and cleaned the throttle body (including internal passages) and checked/cleaned its idle air control solenoid?

I'm not the original poster but my answer is never, thanks Albert.

OOPS... sorry...

In the nearly 400,000 miles I've driven my Riv, every so often I have had to remove the throttle body and clean the backside along with its internal passages.  Different cars would have different mileage intervals for this.  If you burn top-tier premium you will have to do it less often.  If you use a coating-safe throttle body cleaner you will have to do it less often.

The way I tell when to do this is pretty simple.

Over the years -- the 100% certain sign that I needed to remove and dunk-clean the throttle body was when I'd notice any flutter, even a minor flutter, in the idle when car is idling no-load (in neutral).  Warmed up or not did not matter much except it's more noticeable when warmed up because the idle should be lower.

To do this cleaning you will need a new TB gasket, some spray or liquid TB cleaner (GM or CRC), and it will help to have a set of brass tubing brushes (like https://www.amazon.com/Bottle-Stainless-Bristle-PMD-Products/dp/B007S91ND4)  to brush out the passages.  First drain about 1/2 gallon to 1 gallon of antifreeze, and save it (the TB is wet in these cars).  Remove the accessories (the IAC, the TPS, the MAF sensor)then remove the TB.  Clean off the supercharger inlet (old gasket) and then clean it out (it will have tar in it) along with the little passages (this is important), tubing brush and TB cleaner will help with this.  

Now for the TB.  

You can hold the butterfly open with the external lever pinching the lever tab against the tab on the TB with a locking wrench (vise grip) or small pipe wrench.  It does not have to be hard pinch, just enough to hold it open so you can clean the inside out with a shop rag wet with TB cleaner.  

Use the spray and a rag to clean out the TB.  Use the spray and the tubing brushes to clean out the passages to the IAC etc.   Dress the mounting surface with sandpaper on a wood block if you have to, to get the gasket material off and leave a flat surface.  Clean it off with TB cleaner and blow dry with shop air.  When dry, reassemble everything.

Also, by the way, read through https://rivperformance.editboard.com/t9990p50-car-runs-rough-when-it-gets-up-to-operating-temp, https://rivperformance.editboard.com/t2149p25-mass-air-flow, https://rivperformance.editboard.com/t11906-fluctuating-idle.  You may be looking at injectors, temp sensor, or even spark plug wire issues.

Albertj

A little further on this.

I think if it was injectors the problem would be more or less constant.

I think if it was the fuel pressure regulator, same thing.

It maybe might be fuel pump related but I doubt it.

The idle air control servo may be the culprit, if it has become slow due to age or the pintle is crud-coated. It would make the car act up until it repositions after a warm start.

If you replace the IAC without removing and cleaning up the TB then the pintle will eventually stick differently and you may get an oscillating or fluctuating fast idle followed by a fast idle as the PCM switches among default modes to keep the car running while stopped.

thanks again albertj makes sense , because in the first 20 minutes or so when in drive the rpms are atround 800 rpms with my foot on the brake but when I drop into neutral rpms jump to about 1100 and when the car is warmed up and I drop it into neutral it stays around 800 rpms( just bye lookin at the dash gauge)im sure my TB needs cleaned. thanks again!!also noticed my idle jumps up also when I put my headlight on.

is a Trans Range Selector hard to change on my 95 every so often all gear lights flash until I jiggle the shifter

Rivieraz wrote:

is a Trans Range Selector hard to change on my 95 every so often all gear lights flash until I giggle the shifter

I've never had to do that but I don't think so. There may be a post about that on the site, try using the search function to find it.

Rivieraz wrote:

thanks again albertj makes sense , because in the first 20 minutes or so when in drive the rpms are atround 800 rpms with my foot on the brake but when I drop into neutral rpms jump to about 1100 and when the car is warmed up and I drop it into neutral it stays around 800 rpms( just bye lookin at the dash gauge)im sure my TB needs cleaned. thanks again!!also noticed my idle jumps up also when I put my headlight on.

It is not the jumping you are looking for.

When the car is warm and idling the idle should be steady enough that you can not see the tach needle move. At all. When the passages are a little dirty it will flutter or "hunt" a little. When things are bad it will hunt (hunt = very up and down) a lot. When things are terrible the PCM will force the warm idle to 1000+ RPM and set a code.

You are lookin for that hunting. You want to clean it when the passages are a little dirty because it is *way* easier to clean.

I don't know if you have any codes but I found out my evaporator box is clogged and I have similar symptoms. It may not be the answer but just something to check.

thank you hope everyone is safe n healthy

U too.

getting TB done this week, i'll keep everyone posted thanks again!

Rivieraz wrote:

getting TB done this week, i'll keep everyone posted thanks again!

Make sure whoever does the TB actually removes it and cleans it, and tests the sensors as well as the IAT solenoid.   If you just spray cleaner in the face, it will not get clean matter of fact if you just pull the screen and look it it probably *looks* clean already.  The headache is behind the throttle flap. You can't reach that area with just a spray-in.   If it is not removed and the idle air passages flushed, the idle will not improve.  BTDT.  

Albert

still waiting for my mech,but he a little unsure with it being25 yrs old , he afraid of all the wires hopeing not be brittle and such,sorry to keep you hanging , when things change I will post!stay healthy ppl!

Rivieraz wrote:

still waiting for my mech,but he a little unsure with it being25 yrs old , he afraid of all the wires hopeing not be brittle and such,sorry to keep you hanging , when things change I will post!stay healthy ppl!

I had a problem with the connector to the idle air control... fixed it by gently heating the connector while unplugged so the latch would go back into shape.

as for the chugging at start , i think it was the bypass acuator , has not done it since i replaced it