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95 Seville STS

4.6 Northstar

While driving around 35 mph I can feel the car surging, and at idle I can feel a slight miss. Also if I hold my foot steady on the gas pedal at 1000 rpm's the tach constantly bounces back and forth from 1000 to 1200.

The car is not showing any codes.

I have put new plugs, plug wires, throttle position sensor, fuel filter, checked for vacuum leaks, and cleaned the EGR valve. The intake manifold bolts seemed a little loose to me so I snugged them up.

Any help appreciated.

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not sure if it help in the higher RPMs but at idle it always helps to clean out the throttle body and MAF sensor with carb/injector cleaner. Use a toothbrush and get all around the butterflys in the TB and spray the MAF and use a Qtip if its real bad.

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not sure if it help in the higher RPMs but at idle it always helps to clean out the throttle body and MAF sensor with carb/injector cleaner. Use a toothbrush and get all around the butterflys in the TB and spray the MAF and use a Qtip if its real bad.

I may be wrong, but I thought that using carb cleaner on a MAF sensor could ruin it?

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not sure if it help in the higher RPMs but at idle it always helps to clean out the throttle body and MAF sensor with carb/injector cleaner. Use a toothbrush and get all around the butterflys in the TB and spray the MAF and use a Qtip if its real bad.

I may be wrong, but I thought that using carb cleaner on a MAF sensor could ruin it?

True. One should use MAF cleaner.

The saddest thing in life is wasted talent

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The next things to check are the coils. I think in 95 you can do a power balance check. This allows you to turn off the injectors to see which cylinder may be causing the problem. Here is the power balance check:

1.) enter diagnostics

2.) select pcm override PS04

3.) press warmer button until injector "1" is selected (it shows up in the climate control panel)

4.) press "off" to maintain override, then select pcm data PD11 (rpm's)

5.) press "cooler" button and note change in rpm and idle quality

6.) record change for that cylinder

7.) press "warmer" button until cylinder "2" is selected.

Repeat steps 5 thru 7 until you go through all the cylinders.

If rpm's and idle quality does not change when testing, then that cylinder is a problem. Check or replace the coil associated with that cylinder. You may have to perform this test a couple of times to get consistant readings.

Another way to check the coils is buy 1 coil and replace the coils with the known good coil one at a time until you find the bad one.

Before you do this make double sure that the plug wires are not crossed.

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Thanks Paul, First I double checked the plug wires and all were where they should be. I did the test and all 8 cylinders sputtered worse while holding down the cooler button.

The miss at idle I feel is very slight, not like the engine is shaking bad. The engine runs strong, plenty of power, just the "surging" at 35 mph. Maybe that's not the right word for what it does, it's like your holding it at a steady speed and some how a little shot of gas get's thrown in there to raise rpm's around 200. Can feel the car moving back and forth. Not real hard like a bucking horse or anything. Also at idle in Park if I try to hold foot steady on gas pedal at 1000 rpm's, you can watch the tachometer go up to 1200 then back to 1000, 1200, 1000 constantly.

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I had a similar problem with my 94 SLS. It drove me nuts!

I tried replacing plugs & wires. I cleaned the throttle body and removed the intake and cleaned all the small EGR passages, replaced the fuel pressure regulator, & still had the intermittent miss at about 55 MPH. The miss would go away when I accelerated or decelerated. The engine was STRONG! I could routinely show Mustang 5.0 owners my taillights. BUT that darn miss would go away!

I finally asked an old Cadillac tech to look at the car. He found that there was corrosion on a couple of the coil pack high tension terminals VOILA! No more miss!

As I recall, he used a small piece of Scotch Brite on the end of a pencil eraser to clean the terminals.

I hope this is your problem too. It is an easy fix for no cost.

Take Care,

Britt

Britt
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Thanks Britt. I removed all plug wires from coil packs and used a piece of steel wool to clean the terminal's where they plug on. They didn't look that bad but did it anyway to eliminate that problem. Car runs the same, this is driving me nuts also.

I also added a can of Seafoam to the gas tank, but as of right now car still has slight miss and engine surge around 35 mph.

Any other ideas?

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You said the car is not showing any codes

Have you checked, adjusted and cleaned the ISC motor? Check this thread

http://caddyinfo.ipb...?showtopic=7605

Given the age check the throttle body's throttle plate for looseness or wear that will allow a vacuum leak at a certain throttle angle

As far as the mis, it can be anything, if you can get an engine analyzer you can hone in on which cylinder is giving you the misses, but this can also be done by a power balance test detailed above to uncover the bad cylinder. Anything that can impact air, fuel or combustion/compression can cause it, you just need to eliminate one thing at a time

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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You might check under the coils to see if the connection tabs are corroded. I had this same problem for about 6 months, miss under light acceleration. Power balance test did not catch it until a coil finally died. I could smell plastic melting and smoke started coming out from under the hood. At this point I was ready to let her burn, but it was just the bad coil shorting out. Buy a good coil and replace them one at a time until the miss is gone.

Edited by PAUL T
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Yes The car is NOT showing any codes, I checked again today.

Ok Today I took the idle speed control off and took it apart, cleaned all old grease out, cleaned the contacts, and added new grease. Also I followed this video on how to test it http://www.wonderhowto.com/how-to-test-replace-idle-speed-control-motor-251782/ It tested good according to that so I reinstalled it and car runs the same.

Tomorrow I will take the coils off and see what they look like underneath. I hate to go buy a new coil, waste the money, if that's not what it is. I can see one was replaced by the previous owner, as it doesn't have the cylinder number's on it.

I'm wondering now if the fuel injectors are clogged a little or something. If they are hopefully the Seafoam will clean them out!

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Buy one coil, check things out, and if that is not the problem, take it off and take it back for a refund. Save yourself alot of grief. If one coil has been replaced then the others will follow. A coil problem will not show a code until a coil finally gives out.

Edited by PAUL T
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Took coils off today, connections underneath didn't look bad but I cleaned them anyway. Car still the same. The miss is not real bad, most people probably wouldn't even know it was there. Maybe the surging also, but I can feel and hear it, and it drives me nut's. Car run's strong, plenty of power, bark's the tires when shifting, not like it is running on 6 or 7 cylinders. An older guy had it before me, maybe I just need to get it out on the interstate and try to get a ticket lol.

I started thinking about the rubber O ring gasket where the throttle body hook's up to the spacer, I sprayed carb cleaner around it and the idle didn't change but maybe it is leaking underneath. I'm going to order 1 (part store is out of stock) and replace that and check and make sure I got everything clean in there while I have it off.

Any other ideas appreciated, Thanks to all.

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Most places will not take back electrical parts.

Advance Auto has taken back electrical parts from me before.

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  • 2 weeks later...

Last week my mom borrowed my car and when she pulled in the driveway the car died. It would not start without holding foot on gas so I checked the codes and got P026 P095 and S036. I took the throttle position sensor off, returned to Autozone and exchanged it (had only been on the car for 3 weeks) cleared codes, car runs and starts fine except the surge at 35 mph and slight miss at idle.

As far as I know there is no adjustment to make when replacing the TPS, I just put it on, had to turn the sensor about a 1/4 inch to get it to line up to put the screws in.

S036 is electronic level control compressor short to ground, why would that code show, and it couldn't have anything to do with my surging could it? The only time i ever hear the compressor run is when I press warm and off to check for codes it runs for a few seconds

Checked codes today after driving several days and have none showing.

I have been having bad luck with new parts, last month the alternator died after being on the car for 9 months. I bought it from Advance Auto because dealer part was a lot more. I have read only to buy from dealer so if this 1 goes bad I guess I will have to pay the extra cash!

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I have been having bad luck with new parts, last month the alternator died after being on the car for 9 months. I bought it from Advance Auto because dealer part was a lot more. I have read only to buy from dealer so if this 1 goes bad I guess I will have to pay the extra cash!

I learned the hard way too. I only use OEM parts now. Aftermarket parts are just not the same quality. I usually get my OEM parts from rockauto.com ,they are about as cheap, pricewise, as aftermarket. I still say swap out the coils with one good one.

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