Moved from http://driveonwood.com/forum/1651 (Dakota - common intake manifold problems)
Does anyone know if something like this is likely on a TBI 350 Chevy engine? My '95 K1500 has started showing those same symptoms. Thanks in advance.
Brian
I don’t think chevy ever use a split intake like this on tbi. Check your egr system, timing, vacuum leaks, pcv system first.
Marvin
like Marvin said, no plenum gasket on a TBI chev. With no obvious oil leaks most likely eating up oil through worn valve seals. Chev/GMC shouldn’t ping as they have a knock sensor on the block that retards timing when it senses pinging. (OBD1 dodge does not have this sensor). Chev/GMC shouldn’t ping but run like a turd if the sensor picks up pinging or is damaged.
I guess I’m not actually sure what pinging sounds like on a V8… Every other vehicle I’ve owned or driven has been an I-4 (or H-4 in the case of my Subaru). I know I’ve heard it on my dad’s old '88 Toyota 22-R carbed engine.
Here’s my Chevy symptoms: Sometimes, almost always at idle/low speed (35mph or less in City driving) it will start to “lug down” as my dad would say, almost like the sound of a steam locomotive struggling to a stop going up a hill. It does it equally going somewhat downhill (low load) as going uphill (higher load.
The RPMs will drop below situational normal (like down to 300 on a normal 950 idle, no load) and “sound like it is running like a turd”, as Dustin said… Occasionally, it has died on me while stopped at a stoplight. Usually, giving it a quick throttle press will let it recover. It will still usually run fairly rough for a minute or 2. A few times it has done this at idle when I’ve been able to get out of my truck and walk around. I thought it smelled more like it was “running rich” than burning oil, but I’m only “slightly above average” on engine knowledge, which isn’t saying much these days.
It never has had any “visible” exhaust of either blue or black variety, maybe a bit of normal white steam on a cold morning start-up. Almost never has any problems at highway/freeway speeds.
Oh, and I have lost a fair amount of oil recently with no visible fresh leaks, just the normal very slow seepage leaks.
One of these days I’ll manage to take a video of it, but it happens fairly “randomly” and sporatically from my point of view.
sounds like your catalytic convertor could be plugged, also GM had cam shaft that would wear, and cause some of these symptoms. I would pull all the spark plugs, look at the burn color, then do a compression test. Good luck Al
Al: Thanks, I’ll check those out.
Oh the many possible problems that are possible. I have had several Chev that used oil and I was told it was the valve seals get hard/cracked and suck oil. Never have replaced any to see — oil was cheaper than the installation of seals. Yes cams get worn out lobes and they do cause the engine to idle rough. Pull the valve covers and turn the engine over with a wrench and try to wiggle the rockers. If one or two seem looser you have a worn cam and it must be replaced with a new one. Having said all that, you last statement makes me think it could but your EGR (ehanust gas resurculator ) valve. Pull the rubber hose that goes to the EGR and replace it with a different hose. As the engine is idling apply a vacuum to the new hose ( I have done this with my mouth and I could open the valve) If it is working, the engine should start stumbling with the applied vacuum. If it doesn’t, you probably have a bad EGR. Other than that the easiest thing to do is look and listen for vacuum leaks in the many vacuum lines. Follow them all back to make sure they are connected on both ends and not split. Good luckTomC
A cheap fix (that it probably needs anyway) is to replace all your vacuum lines, especially those bright little colored ones. I was hunting a vacuum leak on my '92 F150 and attempted to move the hoses around to see where they went, and they were so brittle they broke off in my hand. Right then, I decided to just pull them all out and replace them with new black rubber ones.
The eac valve on side of tbi?..can get gummed up and not extend or return…causing a very large vaccume leak…also…egr…sometimes gets stuck…and throttle body base gasket…can crack…
easy EGR check is while the engine is running push the diaphragm of the egr up and the motor should stumble, if no then a bad EGR. (this is the same procedure as mr Tom Collins is suggesting but without having to suck on the temporary vacuum line to make the diaphragm move, can be easily tested by compressing diaphragm by hand. Also EGR check can be done with with engine off and compressing the EGR valve by hand once again and then putting your other thumb over the vacuum port. When you release the EGR valve diaphragm from compression it should stay were it is (in compressed form i.e its holding vacuum) if it returns when you still have your thumb over the vacuum port then its a bad EGR.
No brainer here but have to mention. Does it throw any codes, if so which ones.
It hasn’t thrown any engine codes in the time I’ve owned it. The Anti-Lock brake light has been on “forever”, and a parts shop scanner said there was an old code for the Idle Air Control Valve, which I’ve cleaned to no benefit.
I have a 91 k2500 with 350 tbi…was not idling…plus would nose dive or hesitate on acceleration from a stop…unless I feathered the gas…cleaned iac…replaced baseplate gasket…blocked off egr…still idle issues…adjusted distributer…helped starting…but still idle issues…sprayed carb cleaner on every possible vaccume port…still idle issues only after replacing iac…twice (don’t buy off ebay) did it correct my issues…idles great and…Now accerates like it should.
Caveat: I am currently on vacation in China visiting my brother so I can’t look at my truck or test anything for another 2 weeks.
After some thought, wouldn’t a plugging Cat cause more problems at high-end than at low-end? I mean there should be a lot more exhaust moving through the Cat when at WOT trying to pass a car at 60mph than there woud be while idling to a stop or feather-cruising at 20mph through a School Zone. Truck does fine while driving heavy on the throttle and at higher speeds.
Looking at IACVs, I might as well try to swap it out. Unfortunately, I have 2 auto-parts stores in my town: Autozone and O’Reilly.
Autozone only has 1 unit available, a DURALAST, which is 52$ with a single review of 1 star saying that he had to replace 2 of these in a year.
O’Reilly is a company that has repeatedly shown that they aren’t a company I want to support. They do have 2 units available, but neither is a brand I’m familiar with and neither has any reviews: MASTERPRO IGNITION for 41$ or the BWD for 45$.
It seems nobody makes a “set” of vaccuum hoses to replace the lot. My limited Google search abilities (have to VPN into Hong Kong and then use the English google.com.hk site) haven’t come up with anything helpful. Does anybody have a source for finding out how many feet of “X Dia.” and how many feet of “Y Dia.” hose I’d need to replace all my vaccuum hoses?
If you’re going to spend that much, go ahead and get the AC Delco brand from Rock Auto for $48.99
http://www.rockauto.com/catalog/moreinfo.php?pk=88853&cc=1051063
I’m learning my lesson on Chinese knock-offs. I had a simple horn relay from O’Reilly’s last less than a year with VERY minimal usage, and ended up replacing it with one of my original 23-year-old Ford relays. Of course, nowadays, even the so-called American brands are made in China, but hopefully with better materials and tighter tolerances. Hopefully.
As far as the vacuum lines, you need to determine your inner diameter(s),then just buy them by the foot as needed. No kits exist that I’m aware of.
AT in TX
my next door guys truck is a obd2 1998 1500 chevy we replaced all typical parts at no avail, untill we replaced the engine coolent sensor, it ran like crap or surged and stalled/probley wont help on 1995 not surel I would at least test the sensor/or check for sensor trouble shooting.TRY UNPLUGING THE SENSOR. IF it is shorted it, will start running better just unpluging it, except it ran rich untill the sensor was replaced. THAT 1998 sensor is on top in front of intake manifold.
BWD at O’Rylies is Borg warner
Too much info. I tried to read all the posts on this moved site. I had to install a solenoid on my 93 4.3 L chevy for it to idle right on woodgas … The idle bypass could not handle it and open up enough. I’d post a picture link only my website disapeared. I set the idle speed with it on at 2500 rpm on gasoline. It would idle steady at around 1000 on woodgas. I used an antidieseling solenoid off an old quadrajet carb. Very easy to mount with one piece of flat steel and a couple of holes. The 4.3 is the same as the 350 minus 2 jugs. There is a split in the intake with the 2 barrel TBI. If you turn one injector off it won’t run for poop. Regards, Mike LaRosa
I finally caught a video (sort of) of my rough idle. This was after driving about 3-4 miles, with some uphill sections, and was at normal operating temps. I don’t think it’s ever happened when the engine was cold. Just sitting in D with my foot on the brake, nothing on the gas. If I shift into N, it doesn’t matter.
Sorry about the sideways/tall video. I was scrambling to get my phone out to video it while at a stop sign with people coming up behind me. Somehow, my phone thought that I wanted a sideways/tall video.
- YouTube Hopefully it works, because I haven’t found anything about the “Publish” buttons I’ve heard other’s talking about.
Kept it at only 10 seconds (because of car coming up behind), so hopefully even Steve U. can see it.
Brian, The EGR valves sometimes get stuck open. I carry a pipe around to bang on mine when it sticks … I hope you read my post above yours. I can’t watch the video. Sorry, Mike
Hey BrianHam
I can actually now wifi at the Library do video fine.
MikeL is corect about EGR valves sticking open on these.
Do realize that engine idle is the absolute minimum air needed flow condition.
ANY false air (unexpected/unneeded) into the intake will cause this idle speed hunting problem.
EGR valve sticking open, PCV gummed up sticking, Canister Purge Valve sticking open, base of throttle body air leaks, intake manifold air leaks (can change from cold to HOT, heated up), cracked hoses in-line to some of these if a divorced remote mounted.
Some systems (not this GM) even a dirty, sticking, slightly opened throttle plate will cause this.
Been nailed by all of these.
Intermittent what makes it tough to isolate.
Wishing you perseverance and patience.
Regards
Steve Unruh