i have an 89 deville with a bit of an acceleration problem. this started out gradual and is getting worse. the car seems to idle just fine, and in park, i can rev it up without it missing. when i'm driving is when it stumbles and misses. if i'm holding one speed, it seems to be just fine, when i give it maybe more than 1/5 throttle, it starts to miss and stumble really badly.

-This pretty much seems to happen once it warms up
-The check engine light never comes on

I have diacom plus, so i hooked that up and went for a drive tonight. I just replaced the egr valve and vacuum solenoid, and i can confirm the egr valve is opening/closing correctly and not leaking. This problem precedes the egr valve and solenoid being replaced. The tps sensor is around .58volts at idle and increments smoothly to 4.25 volts at WOT so that seems to be working correctly and is in adjustment. Idle is at around 700 rpms. The map sensor reads about 9hg of vacuum at idle and up to 30 during normal driving. As far as i can tell it seems to be operating correctly.

The only thing i haven't been able to verify is fuel pressure. there is not a schrader valve i can see to hook a fuel pressure guage to. I have not replaced the fuel filter in some time. I did pull the breather cover off and start the car to make sure the spray pattern on the injectors was good and it did appear so.

Two things i'm wondering about are vacuum and fuel delivery. if i had a vacuum leak bad enough to cause this, wouldn't i have problems at more than just acceleration and wouldn't i be seeing map sensor readings different than what they are?

As for fuel delivery, i had the gas tank out about a year ago to replace a large portion of the fuel lines. i cleaned out the tank, cleaned out the internal screen, and changed the fuel filter at that time. could this be a clogged fuel filter causing this?

Also, it's been since last summer since the plugs and wires were changed. The air filter was changed 2000 miles ago with the oil and filter.

I just put a brand new cat-back exhaust on it last week. the cat is about 3 years old. it is a catco. problem precedes the exhaust work. could a clogged cat be causing this?

I'm likely going to change the plugs, wires, and fuel filter wednesday as i have all of these parts sitting around.

That's all i can think of. any suggestions would be appreciated.

Sounds more like plugs & wires to me. Don't overlook the distributor cap. Over time the contacts will get erroded and the gap becomes too large between the rotor and the cap contacts.

i replaced the fuel filter, cap, rotor, plugs, and wires tonight. the car runs alot better because the plugs looked really bad. the contacts on the cap and rotor button were also a little corroded.

This did not fix the problem though. The car runs much nicer but the car surges when you give it 1/4 - 1/2 throttle. it will just sortof sit there like it has no power and then take off. This is actually what the car started doing before the miss on acceleration started.

I'm still curious about the catallytic converter. that and the timing are the two things i am wondering about now. could timing issues be causing the hesitation on acceleration and eventual fouling of the plugs?

what concerns me is the plugs had a white powdery residue all over them. all of them did. The electrodes did not look worn down or anything. Anybody know what would cause the plugs to foul like this?

still open to ideas and suggestions

Thanks

pjunod,
my caddy is doing the exact same thing. I replace the fuel filter, plugs, cap and rotor and I still have the same problem.

I just drove the car around in the Tucson heat and when I got home it just started stumbling in idle. I kept it running, popped the hood and pulled of the air cover unit and saw that the isc motor was kicking in and out. Something new!

So I have a list of things it could be and if you or anyone else could help solve this puzzle? :

Fuel relay:
when the car started to act up, I just happen to have the passanger side dash panel down and could hear that the relay made a loud clicking noise when the gas would kick in and out.

ISC motor:
Since I saw the ISC motor kicking in and out so fast, I think I will do some testing to see if it works right.

CAT. Convert
could be clogged? There was a little pinging noise coming from the car. Not sure if it was in the fuel/engine or converter? It did not make the sound for long.

For now, I am going to set the timing and get me a fuel pressure gauge for gm throttle body and run a test. I will let you know if this solves my problem.

Thanks

Bluesgirl,
If the converter was clogged it would run very sluggishly if at all. Worse at higher RPM.

ISC motor definately sounds like it is on it's way out. Does it ratchet when shut down?

EGR will cause idle problems like you discribe.

I noticed you replaced all ignition parts except the wires. Do the mist test in the dark and see what happens.

thanks for the info Ranger,
I did change my cat. converter and it was bad but not the problem. The car started acting up again and I noticed the fuel injectors would spray and both of them had a drip. So I am thinking it is the injectors.
I plan to check the timeing again and clean the EGR today. I'll see how that works.
Not to sure what the mist test is could you explain that to me?
Thanks again
Bluesgirl

thanks for the info Ranger,
I did change my cat. converter and it was bad but not the problem. The car started acting up again and I noticed the fuel injectors would spray and both of them had a drip. So I am thinking it is the injectors.
I plan to check the timeing again and clean the EGR today. I'll see how that works.
Not to sure what the mist test is could you explain that to me?
Thanks again
Bluesgirl
Wet wires will arc if they are bad. You can see arking in the dark.

I learn something new every day! Thank you all for you help. Maybe today I can get my daughter caddy fixed so I can have mine back!
Thanks again

Update,

I still have the problem! Car stumbles when hot, stumbles when you turn even with a full tank and will flat out die when it gets real hot outside 100 degrees. In some cases it starts right up and others you have to wait a few minutes.
I have replaced the fuel filter,Isc motor twice. First one I bought from auto zone was bad. I followed the correct installtion process ie. retracting the motor,.30 gap..., I also replaced the plugs- with correct gap, mist test on wires, replaced cap and rotor, replace cat and 02 sensor, and have done the timing so many times I can now do it by feel. I also check the EGR and it works. Also cleaned TB.

I took the weekend off for drinking and swearing about my daughters caddy. :alchi: But that got me no where. By the way I conveinced my daughter to buy this great car. I have an 88 deville and it runs great! Please if anyone has had this strange stumbling problem or has insight please help.


This morning I thought maybe it is the sensor in the air cleaner cover where the vaccum hoses connect to and boy did it have alot of dirt and carbon on it. I Pulled the air cover off and drove 4 miles in 84 degree weather, the car ran ok. I had no stumble but the car ran ruff. The best part I was getting 19.8 MPG (Ture Story). The part cost 80.00 I decided to try and clean the old one or go to the junk yard.


So this leads me to check the MAP sensor. With the harness disconnected I get 4.98 volt, with a back probe I get 2.9 volt up to 100ish and then zero.

I pulled the parameter codes from the ccc and this is with the engine running and the car at running temp.

P.01 - .5 *
P.02 - 30-31
P.03 - 93
P.04 - 94
P.05 - 94
P.06 - 1.3
P.07 - .65 .66
P.08 - 12-13
P.09 - 42
P.10 - 13.5 *
P.11 - 80
P.12 - 0
P.13 - 4 ,5,3,7,3,1,0,6,14 *
P.14 - 122-124
P.15 - 76
P.16 - 1
P.17 - 344 *

* These are the only parameter I understand. Not sure if any of these parameters should be at a certain setting.


So todays conclusion is:

02 sensor - Yet another part from autozone I need to R&R. This part is one week old.

MAP sensor - I need to replace. junk yard trip


I must say I do like the gas milage.


Can anyone help solve this problem?
Thanks
Bluesgirl