Random Surge at Idle

[bl78ljb]

Well, I know I have read something about this on the forum in the past, but have been searching for hours and cannot find it. My '98 Burb has an occasional surge at idle. Typically the truck is sitting parked and idling (more with the cold temps) and suddenly out of nowhere the engine sounds like it is surging, and then goes away as quickly as it started. I have not seen an bump in RPM when this occurs and I cannot predict when it will happen. On occasion it seems to be twice in one day and other times it may go weeks before it happens again. If I recall correctly I read somewhere that this might be related to a transmission sensor?? Any help would be appreciated as this is annoying, though not an urgent repair.

[More Power]

Fuel filter? Lift pump?

Jim

[bl78ljb]

fuel filter is changed every 3K miles (just changed 400miles ago) and the lift pump is working fine. I have had issues with both and this is way too random to be something like that it seems more electrical / electronic and it is a sudden occurrence almost as if the engine was loaded then load was released for a split second and then reaplied with no movement in the tach as I think it occurs too quickly to make a difference in actual RPM.

[DennisG01]

Hmmmm. Very interesting that you posted this. I just had something very similar. About 25* outside (about 15* overnight), started fine - very little white smoke (plugged in overnight). Put the high idle on to let it warm up and started to walk back inside. It started to "miss". Did it for about 1 minute - maybe every 5 - 10 seconds. Then it stopped. Drove fine for the 20 minute ride to work.

Anyways, I started searching through the posts - using the keyword "fishbite" as I've seen that term thrown around before. Did you try that term? The only problem is, from the posts I've read so far, it seems as though "fishbite" goes along with hot temperatures, not cold like you (and me) are experiencing.

As of right now, I'm just going to mark it up to "weird things happen in cold temperatures".

For the first 30 seconds after start-up, or so, my speedo needle will jump around. This has happened for quite some time and I've also just attributed it to cold temps. Does this happen to you, also?

ps: not looking to hijack your thread - just wanted to post to say you've got someone with a similar situation.

[bl78ljb]

I have had fishbite before and found the problem / fixed it. The problem I am having is even more random and only occurs one time at idle and then doesn't happen for possibly days again, and is temperature neutral. Fishbite also usually occurs while driving as well, and mine has never happened while driving only sitting at idle.

[DennisG01]

Fishbite also usually occurs while driving as well, and mine has never happened while driving only sitting at idle.

OK. I didn't know that. So I'm not experiencing fishbite, either.

You said "temperature neutral". Do you mean it will happen regardless of engine temp, or outside temp? In other words, will happen at idle with a warm engine?

[bl78ljb]

I was more thinking of ambient temp, but I do think my issue only occurs when the truck is warmed up, but to qualify that I don't leave the truck idling much cold as I don't have a high idle yet and it doesn't warm up idling.

[DaveNY]

My truck has done that same stunt for as long as I can remember. I have had three FSD failures and one pump replacement and it still does it so I have just made peace with it. I have put approx 70,000 miles on the truck since I bought it and nothing has reared its ugly head yet! So I just let it have a little episode now and then and we get along fine.

[Robyn]

With the number of sensors and related electronics onboard, these little creatures can do all sorts of little things.

Its could be an electrical "spike" or electrical "Noise" that causes a momentary glitch in the control system.

If its mostly when warm????????/ Possibly a faulty coolant temp switch that is sending a goofy signal.

Could be a ground that is slightly corroded.

Just far too many things "Could" cause this.

Now|||||||||| it is possible that you caould have one injector that has an issue at slow speed. This could cause a slight issue with idle speed which the ECM will try and correct quickly by adjusting the fuel and timing settings.

This condition could cause a slight variation in the idle speed and hence the sounds you hear.

Finding this gremlin may be an excercise in futility though, seeing as how its so random.

An engine speed sensor could cause issue and if its not cronic the ECM may not set a code.

Keep us posted

RC

[bl78ljb]

Robyn,
Thanks for the suggestions. I agree in the potential exercise in futility with the randomness. As it is not on the top of my priority list I will check on those issues over time. The main reason I asked to begin with is because this was bugging my wife who normally drives the Suburban. On an interesting note and possibly related - only time will tell - We ended up at Sears the other day because of melted battery cables. Basically I had done the battery cable modification when I purchased the truck and recently both of the batteries died under warranty with the cold temps we have had and when replaced apparently the tech didn't properly tighten the cables and with the current draw and loose connections caused enough heat to destroy one of the cables completely. Now that is fixed I will have to see if this happens again. May have to wait until I can drive the truck enough to determine it isn't present.

[paradit]

Total lurker, you may remember my post "ECT/transmission problem solved"

Anyhoo, I have a new gremlin and it sounds similar to this. Happened tonight on my way to work, chillier than normal, about 4C. Felt the little shudder at about 70mph, knew it wasn't normal. This has happened maybe 4 times to me in the past 1.5 years i've owned the truck - so i knew what was coming next.

My chain of events are - high speed shudder, engine rpm surges up and down, check engine light comes on, big clouds of black smoke with each upward surge in engine RPM, engine enters cold advance timing and gets REALLY noisy. The CEL says "engine performance" or something (can't remember). other contributing factors include:
- noticed today for some reason battery voltage was slightly lower than normal (sitting around 14V when normally its over 15V)
- cold snap hit us today, 23C yesterday, 4C today
- just filled up earlier in the day, and it was pretty empty (fishbite threads say this may be the culprit)
- haven't used any fuel additive in a long time

the only other time my engine acts funny is if I'm driving say 40mph then brake really aggressively. the engine surges a few times once stopped, and if i'm not standing on the brake it would actually lurch forward....not nice.

anyway, if i turn the truck off, wait 5 seconds, and start it up again (even on the highway [shift to N, off then on]) the cold advance cycle disappears and engine runs normally, but CEL stays lit for a few days then disappears.

any suggestions?

Tyler
Edmonton, AB

[paradit]

just an update

my suburban stalled (for the first time ever) while going slow through town. started up again, drove 20 feet, stalled again. towed to a good mechanic who pulled the crank position sensor code. ignored it as he thought it was PMD. good call. changed the PMD (stanadyne) and the suburban just towed my 5000 pound trailer 600 miles through the rockies to get home without a hiccup. so the CPS code can mean bad PMD apparently.

Tyler
99 GMC Burban. 4" exhaust and crossover. guages. new PMD (not remote mounted - which in the literature from stanadyne they say to avoid doing). good truck, but probably going up for sale soon.