Rough Idle - Chevy 350 TBI

[DerekTheGreat]

Hey everyone,

We bought an '89 Chevy K1500 with a 350 in it and 224k miles, with the nasty Getrag trans I knew nothing about until after purchasing the truck. Anyway, we have been chasing a rough idle ever since we got it. Well, it didn't seem to idle rough until a few weeks after we bought it haha. It will idle around 550rip'ems but it's pretty rough. At the exhaust, the best way I can describe the sound is like "chuff chuff chuff chuff" However, I've pulled the plug wires one by one and it only gets worse, like a true dead cylinder. The roughness clears up with more rpm and it runs strong above 1000 rpm or so, great runner on the freeway.

So far here's what I've done to it so far:

-Throttle body has been rebuilt
-New A/C Delco plugs(CR43TS), wires, cap, rotor & Duralast gold dizzy
-Ran about a half gallon of water mist through it to clean the combustion chambers.
-New valve seals - still burns just as much oil too, only you never see blue smoke out of the tailpipe
Seems to burn more oil past 2k rip'ems, almost none below 1,600.

From my limited research it seems this type of idle is common with an intake leak. I haven't done the carb cleaner test either but I'm not seeing any build up of schmoo anywhere around the intake.
I've verified that the temp sending unit is OK with a scanner, for what that's worth. Anyone else experience this? Is it something mechanical maybe? It does have a bunch of miles on it but still pulls great on the expressway and around town, it will roast 'em through second if willed. No ticks, knocks or smoke out of the tailpipe at any rpm, least not that I've noticed. No CEL either. I haven't checked timing chain slack but I'm running about 1* advanced base timing. No tools to do compression check yet it was either OK or the shop lied when they said they put new valve seals in it...

 

[MouthForWar]

From what I've gathered, rough idles or occasional misses at idle are really common with these trucks, and they're usually all over the place as far as cause goes. I'm currently chasing an occasional stumble at idle on my '92; no CEL.

The good thing is that sensors and such on these rigs are pretty cheap, so I went through all the basics first. I just recently got the truck and it needed a lot of things replaced anyway. O2, IAC, CTS, plugs/wires, rotor/cap, etc. Still didn't solve it. Eventually I went the same route you're thinking and did the intake mani gaskets....holy cow those things were ridiculously grenaded.

Having said that, I can't report whether or not that fixed it, because I still don't have it put back together, haha. (Need to replace my injector pod and a fuel line for other reasons, lol). Just wanted to jump in and say you're headed down the right track as far as what I've seen is typical with these engines.

If the bad intake mani gaskets weren't causing my issue, my next step will be the TPS and the MAP.

Maybe we can chase our stumbles together. Haha.

 

[DerekTheGreat]

I'm seeing the same thing.. Seems every aging V8 benefits from new intake gaskets.

With our GMC I went and replaced every sensor to try and troubleshoot a surge the thing had and that fixed nothing. Was also my typical process in getting to know a vehicle and establishing a baseline. I've gotten sensors that were garbage right from the get go and have had better luck with old junkyard units that were still operating correctly so now I just use my scanner to see if they're all chooching like they should. After putting Seafoam in the oil ~250 miles before changing the oil and cleaning the combustion chambers with water mist right before said change the truck does seem to be stronger on the expressway and oil consumption seems to have gone down entirely. I also switched from Valvoline SynPower 10W-30 to 5W-40, could have something to do with it. Engine was nasty & neglected before we got it.. When I went to change the plugs, wires, cap & rotor I found out the old dizzy was worn out, you could wiggle the shaft quite a bit and with the new rotor it didn't want to idle so we had to slap a new dizzy in from the chinamen express. Right after it kept setting codes for the IDM module, code 42 or 43 yet there were no breaks in the wire or what not, well it would spark knock a bunch and then set the code. Doesn't do that any more yet if you put your foot to the floor in a gear where you should be down shifting, you can feel it surge a bit. It's very similar to what our 454 TBI did. I think that issue and the rough idle are the same thing.

Let me know if the new gaskets fix your issue once you button it back up. Those are next on my list.

 

[MouthForWar]

Yea, that's basically how I approached this truck (along with any old-but-new-to-me vehicle) too. It was a heavy duty work truck and needed some TLC anyway, plus I was largely unfamiliar with this engine/these trucks. So I just went through and did all the basic maintenance and sensors. Needed to tear down, clean, and rebuild the TBI anyway, so once I was at that point, might as well pull the mani too. Haha. if it it fixes it, great. If not, it needed done regardless plus I got good feel for everything on the top end.

Might be a couple of weeks, as I'm tapped on cash (right after doing all this, the VVT solenoids went out on my '08 Ford Fusion, which I need for work) and a new inj. pod and fuel line for the truck is gonna set me back another $150-ish. But I'll definitely report back with my findings when all is said and done.

I'm debating throwing some SeaFoam in both vehicles, as they both have a sludge issue (for different reasons) and for the first time ever, MOA didn't do the trick. I'm a little wary of using SeaFoam in the crankcase of engines with so many miles though (240k on the car and 295k on the truck). I might just do like a quarter can, and a few short O.C.I.s.

 

[DerekTheGreat]

Oh yeah, I'm real familiar with "I'm here so might as well do this and this.."

Welp, with the injectors they either work or they don't from what I've gleaned & experienced. If they spray like doo then when you take the TB all apart give them a thorough cleaning. That's what I did with the 454.

MOA? Seafoam says to use 1-1.5oz/qt and I used about 1.5 on the truck. Claims to unstick lifters & oil rings. Our truck doesn't tick or make any noise but it does burn oil, up to 1qt every 180 miles or so... I decided to use it after watching this dude's video:

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Oil pressure seems higher and more consistent but that could be due to the thicker oil and sending unit.. Seafoam itself won't hurt anything as it's just isopropyl alcohol and mineral oil, why I was skeptical about it but after that video I figured, why not?

 

[MouthForWar]

Yea, I've used SeaFoam in the fuel system before with great results; just never dumped it in the crankcase. I've heard of guys taking that too far or running it too long and severely messing things up lol. But between the sludge issues in both vehicles and the oil pressure in the truck consistently being pretty low, might have to give it a whirl in the crankcases.

MOA is an oil cleaner/additive that I pretty much swear by (under normal cirumstances). It's made by B-G, who also makes a fuel additive called 44k that is the bees-knees...better than Lucas even (imho). But yea, for some reason I've got a nasty sludge issue in my car (I run synthetic in both, btw, which makes it even more surprising) that even MOA didn't solve. Time for more drastic measures. Haha.

 

[DerekTheGreat]

I'd do it again if I get another vehicle like this truck, I'm a believer. Watch that video too.

OH, I like BG44k, stuff does work great. I am not a fan of Lucas Mucus whatsoever, oh wait, except for their chain lube, I like that.

What synthetic? I love Valvoline SynPower with Purolater Boss filters, in tests it edged out Mobil One. What are your oil change intervals? I tend to go 3-6k or when it turns dark..

 

[MouthForWar]

I pretty much stick with Castrol Edge/Syntech at this point. If I absolutely have to, I'll run the GTX High Mileage Synth Blend in a pinch.

For about a dozen years, I've worked in delivery/transport, and for the last 7 years I've owned a taxi company...pretty much the most abuse an engine can take, with high mileage to boot. Castrol's oils have been the only ones that have consistently performed well for me over the years under such conditions in a variety of engines....so naturally I use it for my personal vehicles too and have never had an issue (until now I guess, haha).

The car: I currently still run the factory recommended 5W-20 in my Fusion. In light of recent issues though, and the high mileage, I may bump up to 5W-30 or 5W-40 to see if that prevents some of the gelling and high temp cooking. Another factor is that that car is used as a taxi full-time as well now, and is starting to see a lot more high temp idle time than it has in the past. So the heavier hot weight may be beneficial. We'll see. I've never seen this kind of sludge happen in a newer, well-maintained engine with any synthetic oil, even under duress. It's pretty perplexing. The Duratec engine has been bulletproof otherwise, so idk what's going on.

The truck: I have no idea what the PO of my truck was using, but likely still the factory recommended 5W-30. I bumped up to 10W-40 for a few reasons, but only put about 500 miles on the truck before I tore it down. So we'll see. It did seem to help my oil pressure a bit in the beginning of the cycle. I can't get too crazy with the weight though; in wintertime it routinely can hit -30 to -40 here and fluids just turn to absolute sludge. Even block heaters only help a little bit during the really bad cold snaps.

For filters, I've pretty much stuck with the white K&N filters on everything I've owned for years. A bit pricey, but well worth it IMO. I've cut more than my share open and they definitely do the job better than some others (*cough* Fram, Wix *cough*).

Oil & filter change intervals: I tend to stick with around 3k on personal vehicles (even with synthetic), but I'll short change down to 1500 for the taxis or delivery vehicles. I'm pretty **** about keeping clean oil in there, which is why these sludge issues are driving me insane.

Side note: I tried Mobile-1 oil and a Mobile-1 filter years ago, on a '97 Chevy Cavalier that was used heavily as a full-time delivery vehicle, and in spite of glowing reviews from others that led me to try it, it was AWFUL. It was like someone literally just swiped 20 horsepower out from under it. Hence my near-refusal to try new things now. Haha. I've heard good things about Valvoline, but I just can't bring myself to change brands.

On Lucas: Really? I've always had good luck with their stuff...oil and fuel additives as well as power steering additives. I much prefer BG products, but their price tag isn't always realistic...especially on a commercial basis, like in the taxis, where oil is changed freaking weekly and we go through a tank of gas a day. Haha. So Lucas is often a good lower-priced alternative for us. But I turn to BG when the going gets tough or there's a problem. A well-respected local mechanic turned me on to them a few years ago.

I've also had some luck on occasion with some stuff called "Restore" for the oil. Every once in a while on the higher-mileage engines I'll run a can of that through and it seems to help a bit. Anecdotal, I know, but I know a few other guys that swear by it too.

Anyway, this week will be spent doing a few short changes and possibly SeaFoam on the Fusion; we'll see if I can clear out the sludge and if it returns. The truck won't be put together for a couple of weeks though. Spent probably $400 between the two vehicles last week...and contrary to popular belief, taxi owners (well, most of them) don't really make a killing and we often have to neglect our personal vehicles. Haha. Gotta wait for more moolah to order the truck parts.

 

[DerekTheGreat]

Perhaps it's just a myth but the word on the street is Castrol tends to sludge up engines due to it's higher wax content.. I used to run Syntec myself but switched to SynPower after reviewing results done by Scamzoil [Amzoil]. I tried attaching the link but it's not working for whatever reason. If you've got time you could search Google with "Amzoil 5w-30 Oil Test" and see what pops up.. The right thing would show results from a slew of different oils over different tests.

For the newer stuff like your Fusion I would stick with 20 weight as I'm betting the oil galleries are pretty tiny and might not like the 30 weight. I'm also a member on Grandmarq.net and the dudes running 4.6 mod motors prefer Motorcraft 5w-20 over all else, say the engines really like that oil and anything heavier will be too thick for the galleries, which is why I would stay with the 20 weight for your car.

Sounds like you do a good job of keeping up on your oil changes & use quality stuff, not sure what the sludge is about. How's the PCV valve? Does the Fusion use oil? Do you stretch it's legs on the freeway every now and then? Engines seem to like extended operation above 2k rip'ems, helps keep the carbon build-up down too. My old Town Car always runs better & smoother after driving to and back from Florida. I'd throw 1.5oz/qt of Seafoam in it ~250miles before your next oil change and see what happens. My Ferd has lifter tap when cold and since it seemed to help with that one dude's beat-up Ranger and our K1500 I'm anxious to see what it does for our Ferd.

I've tried Luca's power steering **** and it didn't do anything. Tried their trans additive in a friends car with no results. This was nearly a decade ago though, I think I tried more of their stuff back then but can't remember. At the time I basically swore off additives as snake oil but like you I have had good results with Restore & now Seafoam, which I used to laugh at. I still laugh at the idea of using it to clean the combustion chamber. Everyone talks about the smoke show, but all that is is the mineral oil in it burning. From the YouTube videos that show a boroscope analysis of before and after you can see it does nothing. Now, it might help to clean up **** inside your intake manifold or be useful to clean your throttle body but that's about all I'd use it for. I might throw it in the gas tank for those reasons.

How's the taxi business doing against crap like Uber? I hardly see taxi's around here.

 

[MouthForWar]

I ran some SeaFoam through the crankcase of the Fusion this morning, then changed the oil and threw a cheap Microguard filter on it for now (will short-change the filter back to a K&N in a day or two). Did a nice hot drain after the SeaFoam and plenty of s*** -brown, burnt-smelling oil came out. Car runs noticeably better and much smoother, both at idle and under acceleration. I did go ahead and throw 5W-30 in it, but if it shows absolutely any signs or sounds at all of not liking it, I'll back down to the 5W-20 immediately. If sludge continues to be a problem in that engine with the Castrol, I guess I'll go ahead and switch to the Motorcraft stuff, since that's what Ford wants anyway. PVC was replaced a few months ago as routine maintenance (damned thing was over $60; it's one of those heated ones). Car does see a lot of open road and highway mileage as well (usually 50-100 mile trips), so that probably helps. Doesn't actually use oil either.

I have to go back home to Idaho next month to pick up my daughter for the summer; that'll be a thousand-mile round-trip....might take the Fusion and cut her loose and see how she does. It's been a long time since she's been on a really long trip like that.

As far as the biz goes: Uber hit us a little bit, but not too badly. They're pretty popular with the University kids, who were actually never really a big part of our customer base. We're a small town, and we're longtime locals, so we've got a decent crowd of extremely loyal locals that are getting us through for now. We're also pretty comparable on price now, so that helps. Being owner-operators instead of a fleet, we have more flexibility than big-city cabs and can compete a little better. Helps that regulations are pretty lax too and don't handcuff us too much.

As you can probably tell, we're also a little more uptight about quality and such than a lot of big-city cabs (or Uber drivers, for that matter). It hurts the pocketbook sometimes, but I try to stay away from crappy/cheap parts and such on the cabs. Moog steering and suspension parts, KYB or Bilstein shocks, etc. And of course K&N filters and the like. And we've never run the typical ex-police cars or whatever that people complain about; we try to run more normal, comfortable, popular family sedans like this Fusion. And I do a full detail on them every single day.

So yea, it's not easy and we're pretty broke sometimes, but we get by and just do the best we can with what we have and we're trying to change the perception of the industry. We did have to let go of our extra drivers a while back and cut down our hours, so now it's really just the wife driving and me taking care of everything else (mechanical, detailing, accounting, legal, etc). But honestly, it's less stressful in a lot of ways, just having to worry about ourselves.