Last post on Jun 10, 2013 at 7:03 AM
You are in the Chrysler LHS
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Chrysler LHS, Sedan
#1275 of 1409 Re: 1994 Chrysler LHS rough idle [barouk]
Sep 05, 2008 (6:09 am)
I have not yet, got the Idle Air Control Valve. I should have it in a couple of days. I have been a little short of funds like everyone else. I plan to start with that and go to the throttle parts next if that doesnt work. I will keep you posted on how it comes out. My 94 LHS also kind of jumps (is the best way i can put it) when the air conditioning is on. It sort of feels like its jumping in and out of gear but its not. it does the same thing when i am sitting still with the air on. it doesnt do it all the time,maybe like once every 10-20 min. when it happens the rpm's go up and then back down for a sec. I think it still maybe caused by the Idle air control valve though. if its not getting enough air or too much, that would (in my experience) make the idle do wierd things. exspecially if the air is on.
#1276 of 1409 Mystery of the rough idle on the Chrysler 3.5 V5 solved!
Sep 05, 2008 (6:50 pm)
I posted this on Bat auto technical, and a Sr member Danica gave me the first sensible and correct advice on this common problem with the Chrysler 3.5 V6.
Here are the relevant parts of the thread. I posed the same question as above.
Since its an LHS I'll assume its got the 3.5 engine, which has a common problem with lower intake manifold gaskets. This engine has a large upper plenum, and a small intake manifold nestled between the heads. Close to where the upper rad hose fastens to the motor, there is a small area opening to the underside of the intake manifold. Spray carb cleaner in that opening with the engine idling. If it smooths out, you've found your leak.
Thanks Danica! That is just the sort of information I'm looking for. The car is away from here currently. I will have it back next week. I will do exactly what you say, and post back.
If that is it, I will get the gaskets. I bet access won't be brilliant. However when I get the plenum off I might be surprised. Hope Springs eternal! I have the service manual so I will look at the procedure for changing the gaskets. By the way it is the 3. 5.
If you have solved this, your brilliant! I know this is a common problem, and it is all over the net, but no solutions. I have suspected an intake leak all along, but not been able to find it. So to me your reply makes sense.
I sprayed in the carb cleaner just as you instructed. The engine smoothed right out consistently with multiple sprays. I have a an intake manifold gasket replacement coming up! I will be off to the local parts store tomorrow.
Danica, yours was the first correct answer to this problem I have seen on the net.
Should I silicone the gasket, in a addition to the water channel, to prevent further problems?
Once again, thanks for your help. Good job!
Only use silicone sealer on any surfaces that are pitted.
Use caution with the fuel lines and coolant outlet at the rear of the engine.
I finished the intake manifold gasket replacement first thing this morning. Since I have some physical limitations I did the repair over 3 days. I put in three hours two days ago, three hours yesterday, and an hour this morning. So that is seven hours, including radiator refill, warm up air bleeding and testing.
I'm glad to report the engine started right away, with no leaks, check engine lights or fault codes. Best of all the engine idles so smoothly you have to check the rev counter to be certain the engine is running. There are no driving problems at all.
Thanks once again Danica, that was the first sensible advice I received since this problem started.
Since this problem seems prevalent, with no solutions generally offered, I hope this post will pop up in search engines.
Since this seems a significant problem for this engine, I will go into aspects where I had to deviate from the Haines manual.
The most significant difficulty was the fuel rails. The manual says to pinch the connectors to supply and return, but no way would they release. I figured if I removed the thermostat housing I could move them out of the way.
I went to the parts store to get the housing gasket. They sold me a tool to uncouple the rails. However there was an older well seasoned mechanic in the store, and he cautioned me that theses tools often break the coupling, and advised if possible to do the repair without uncoupling the fuel rails. This proved easily possible, once the thermostat housing was removed.
The other issue is the heater hoses on the back of the manifold. The Haines manual mentions only one heater hose. However there are two, and one goes straight down, and I could not get to the hose clamp, as the hose was short and would not pull up. I removed the metal hose connector from the manifold, by removing the two securing bolts. I was able to preserve the gasket, and used blue RTV sealant when I put it back. Otherwise the repair was as per Haines.
Now as to cause. This gasket is brittle plastic. I never saw anything like it. It has finger cracks all over the place. It would soon have caused leak of coolant into the cylinders. It was dreadful to get the remnants off the head and manifold. It is impervious to gasket solvent. I got most off with a razor blade without scraping. For the rest I used the small scotch brite pad on a small air right angle grinder. This got all surfaces clean and shiny. I used form a gasket to hold the manifold gasket, fuel rail gaskets and plenum gaskets in place. A bead of blue RTV sealant was place round all water channel openings. The NAPA replacement gasket looked to be of excellent quality, by the way, and I doubt this problem will recur.
One other issue, I found a mouse nest on the cylinder block, under the inlet manifold!
I'm really glad to have tracked this problem down. These are great engines. I find it strange, that the cause of this common problem with these engines is not widely known. As far as I know this is the only correct answer on the net. Two dealers and multiple experienced mechanics gave me nonsensical answers. I'm glad I left the engine alone, until I was certain what the problem was.
#1277 of 1409 Re: 1994 Chrysler LHS rough idle [barouk]
Sep 07, 2008 (5:56 am)
Did you see the cause and correct solution for this problem?
#1278 of 1409 Re: 1994 Chrysler LHS rough idle [tsurnick]
Sep 08, 2008 (6:06 pm)
I got the Idle air control valve today and installed it. I am also going to try the trick with the carb cleaner, spraying it near the intake manifold. The idle air control valve seemed to bring the idle back up where it needed to be. I will give it a good drive tomorrow to see if the hesitation is still there. It would kind of choke sometimes when the engine was running. Sometimes it would do it on the highway, some at idle. Most of the time at highway speeds. I will keep everyone posted on my progress as well. The other post sounds like more work, but it seemed to fix the problem. My car seems to run fine otherwise.
#1279 of 1409 Re: Mystery of the rough idle on the Chrysler 3.5 V5 solved! [tuscanskipper]
Sep 09, 2008 (5:13 pm)
I did replace the idle air control valve and it helped a little. I got some carb cleaner today and sprayed it near the intake. I started spraying in back near the firewall but no fluctuations in the idle. then i came around to the front near the thermostat housing. When i sprayed there it started to change the idle. it bubbled a little as well. i could not tell if the leak was comming from the intake or the thermostat housing. how can i be sure? I replaced the theremostat and gasket about two months ago and there is no leaks. if the therm housing was leaking, wouldnt it leak antifreeze?. what do you suggest next?
#1280 of 1409 trunck ajar light wont go off.
Sep 09, 2008 (5:20 pm)
i recently put a light in the trunk. i got one of those lights from the auto parts store and unplugged the orriginal light that was already in the trunk. I found out which wire was hot and which was ground. the light works fine but now the trunk ajar light on the dash wont go off. I disconnected the light that i installed in the trunk to see if that would change or fix anything but it didnt. any ideas?
#1281 of 1409 Re: Mystery of the rough idle on the Chrysler 3.5 V5 solved! [tsurnick]
Sep 09, 2008 (6:30 pm)
The thermostat gasket would leak water and not cause this problem. Your problem is failure of the manifold gasket, apparently it usually starts near cylinder No. 5.
When I removed my manifold gasket, I could see why these 3.5 Chrysler engines are known for this problem. The gasket is made of a material I have never seen a gasket made of before and never want to again.
Replace the manifold gasket and your vehicle will be transformed. Make sure you use a traditional high quality gasket, and NOT one of those Chrysler abortions.
If you don't have to take enforced breaks like I do, you should get this done in a day. The complete job took me seven hours.
Time to bite the bullet my friend. If you don't, you will end up with water in a cylinder, and or over heating problems. Mine had to be close on the basis of what I found on my vehicle.
#1282 of 1409 Re: Mystery of the rough idle on the Chrysler 3.5 V5 solved! [tuscanskipper]
Sep 23, 2008 (2:47 pm)
Thanks for the info. I am preparing my self for the job this weekend. I have a slight valve cover leak as well so i plan to do those as well. Would you have any other tips or points to watch out for when i am doing the job sat? I noticed that one of the people posting on here was talking about the fuel Rails? I know what they are but should i remove them or do you have to? It may have been you talking about it. I noticed that the car goes up in idle every now and then, it jumps to about 1200 rpm and back down to about 800 average. when you are sitting still, it just does that. when you are driving if makes the vehicle jump (kind of feels like its popped into gear) but its just the idle speed doing that. I was assuming that this was caused by more air sucking into the manifold . I also need to replace the oil pan gasket, but i may save that for a later day. Its seems easy to get done except for the front area where the bolts are kind of under part of the frame. I wonder who thought of that.
#1283 of 1409 Re: Mystery of the rough idle on the Chrysler 3.5 V5 solved! [tuscanskipper]
Sep 23, 2008 (2:57 pm)
thanks for help but have huge problem. two bolts are frozen and both feel that with any force they will snap. what can i do?