Rpms dropping then recovering

[rockfangd]

Hi all. My 01 Eldo has been doing something weird for a little while now, quite intermittently.

When I am coming down from highway speeds the RPMs seem to drop off a little excessively. enough to make the lights dim a little bit. (probably around 450-500 rpm), then it jumps right back up.

Sometimes it will catch me by surprise as it feels like an engine stall but it does not.

I am not sure if this is normal. Was hoping someone could chime in.

I do not really want to get stuck on the side of the road or worse in an accident(doubt it lol)

I do know that Cadillac had issues with the crank sensors but I do not know if they have been replaced. There has been no codes, stall, or hard start problems.

Thanks all.

Hopefully by the middle of April I will be driving my Seville and can give this car a break.

[Cadillac Jim]

Others will have ideas too. I think that you should look at the serpentine belt to see that everything is tight, and that everything turned by it is free. The alternator may be slipping on the belt, particularly in wet weather after you run over a puddle.

[KHE]

Does the car fall into the range of years that had the issues with the crank sensors made in Mexico? The way to tell is if they have Denso on them, they are the good sensors. If they have Mexico on them, they are the ones that had the issues. It is probably not going to be easy to inspect them but with a mirror or bore scope, you should be able to see the plastic portion where the electrical harness plugs in to the sensor.

When was the EGR valve cleaned last?

[Logan]

There is a bulletin for the Deville...about a problem kinda like this. Just cannot seem to find it right now. I do not know if it applies to the Eldo.

The headlights will dim briefly whenever the air pump cycles. It almost feels like a dead spot in the TPS or brief stall when it does it.

[rockfangd]

It could be that. Now that you mention it I do sometimes hear the air pump kick in when coming down to idle, Pretty rare though.

The belt and tension are fine.

The problem is the drop in rpm. The Rpms are dropping low enough that the load drops. It may be when it is downshifting.

I am not sure if it could be a torque convertor issue (hope not).

I will look into the egr. I plan on putting intake gaskets and plenum boot at the TB. So I will do that at the same time.

The funny thing about this is that it is very random.

Yesterday it did it about 4 times throughout the day.

today it has not done it yet.

[barczy01]

Check for vacuum leaks with propane or brake clean and clean the throttle body. I recently had one of these and crank sensors and a crank relearn fixed it. The problem was more pronounced on a warm engine.

[rockfangd]

There are currently no vacumn leaks. I am going to clean the TB and the egr

[rockfangd]

Well I dont know what exactly did it but I nailed it with my eldo today.

I pulled the intake, cleaned and replaced gaskets,

cleaned throttle body, was awful, had thick black oily carbon built up on the inner side

Cleaned Egr. not too bad

cleaned MAF, nasty

Replaced rear plugs and coil module.

replaced broken pcv hose to front cam cover.

cleaned injectors, replaced o-rings. Still dont care for the plastic type rails.

Replaced the intake coupler. old one was shot.

Cleaned crossover passages, had quite a bit of buildup between the intake and throttle body, especially at the bottom passage.

Now it runs perfect, it accelerates nicely and decelerates great, no more shifting rpms.

Definately has more power.

The engine runs so smooth you cant even tell it is running.

I did find that the left muffler is blown out, that explains the change in tone I was mentioning before, It happened while doing the WOOTs the last time.

So I guess I do need mufflers anyway.

Hopefully with my driving the intake will stay nice and clean. Now I feel it is more reliable.

[Bruce Nunnally]

That sounds like a great tune up and clean up; glad it is running well.