Rough idle on warm start up (20 minutes), 87 7MGTE

[Bru]

I have read the blogs on this issue in the best I could come up with is to try and disconnect the cold start injector.

The issue is on startup after driving car and fully warming up and shutting down for 20 minutes. It idles rough for 30 seconds until I give it some gas then idle is back to normal. It does feel like one cylinder is missing though on acceleration until it smooths out. If I start the car in under 20 minutes after stopping I don't have this issue or if I wait more than an hour. I have replaced the spark plugs and also the idle air valve, and all three coils. Cold morning starts are normal. There is no smoke for loss of coolant detectable. I rebuild the engine five years and 14,000 miles ago. I retorqued the head bolts to 75 ft/lbs. Only a couple moved slightly. Compression is normal. This warm starting issue began in the past couple months. I suspected it might have something to do with the EGR valve because you can mimic a similar condition at any time by applying vacuum to the servo while idling. I disconnected and plugged the servo vacuum line and it's still did the same thing. I thought it might be a leaking down fuel injector so i took the dust cap off of the pulsation damper. The little screw was still in the up position after 20 minutes warm or cold. The spark plug wires are high-quality Bosch silicone but they are 10 years old. I check the resistance and they are all about 1K Ohm each which is well below the 25K limit. It could be a sticking closed injector or valve stem although I have been using redline fuel additives for some time. I also added some Marvel Mystery oil to the oil and fuel with no change noted. The injectors do have 252,000 miles on them. I have checked and adjusted the throttle position sensor and the ignition timing. There are no stored codes. I put in a oil seal replacement kit in the cam position sensor but I can't remember if this issue started before or after.

[cre]

Haven't we already discussed the CSI? Did you test it? Even if the CSI time switch is bad and the CSI is firing whether the car is warm or cold it won't take 20 minutes for extra richness that's only occurring while cranking to clear up.

Ditch the Marvel crap, in the long run it does more damage than good... just run a GOOD oil, try out Penzoil Platinum if you want very good and very cheap. Marvel's just nasty solvents and mineral oil which breaks down under the heat very quickly... Use a good oil and the detergents in it will keep the engine clean just fine and you don't risk releasing any natsy chunks or sludge and debris, it'll be dissolved gradually.

Redline and Techron are both PEA (Polyether Amine) based fuel treatments, run two of either, if that doesn't help and it is the injectors then you need to send them for service. Also, FOLLOW THE DIRECTIONS! It needs to be added to an empty tank (at the gas station, right before you fill up) and driven until near empty before filling up again or you'll dilute it. This ensures a proper concentration and thorough mix. After this only run fuel with PEA based additives (no low grade and only some mid grades usually contain additives, but also check what kind they're using).

Have you tested the KVAFM? Try unplugging it and go for a drive, it'll set codes but the engine should run decently.

With that amount of mileage I'd send the injectors to a reliable shop for cleaning, screen replacement and blueprinting; RC Engineering and Cruizin Performance are the companies I've used in the past with good luck.

Lastly, is the O2 sensor good and connected? All 7M's use a warm start fuel map hat's about 20% richer than the cold start map; As long as the stock O2 sensor is connected this only affects WOT after a warm start.... I've no idea why Toyota did that but it's been confirmed on both the GE and the GTE.

[cre]

http://www.toptiergas.com/index.html

I should add that Techron's concentrated formula is the one you want if you can't find Redline; And that Redline is the slightly better of the two.

[Bru]

The AFM checks out ok (I have 2). The O2 sensor has 50K on it and has tested good in the past. Tonight it did the same thing so I immediately shut it down and pulled the vacuum lines to the fuel pressure regulator and the EGR with out plugging. It started normally. I will have to repeat that to confirm and begin narrowing it down.

[Bru]

I repeated my test by thoroughly warming up the engine and letting it set shut down for 20 minutes with the hood closed. Then I disconnected the fuel pressure regulator vacuum line and plugged it up. The car started and idled normally for 3 seconds then I shut it off. I immediately reattached the vacuum line and started up again and ran rough as it usually does under these conditions. It occurred to me that I had performed the same function as the High Temp Fuel Pressure Up VSV located under the intake manifold at the front of the engine. I've known for quite some time that mine was bad and did not function which means it allowed vacuum to the regulator under all conditions. They go bad by being electrically open. (no resistance at the terminals). Until now this hasn't mattered but I guess it needs it to prevent vapor lock or 10 pounds more fuel pressure making it 40 PSI for the first minute of hot startup. Here's a very informative web page about fuel systems check out page 16. It details the Toyota high temperature (pressure up) fuel control.


www.autoshop101.com/forms/h42.pdf

[Bru]

This engine heat soak issue continues to bug me. I did some research on the web and found out that heat soak maximum temperature occurs between 30 and 40 minutes after shutdown. Another Web site about boat engines recommended running the engine for a few minutes before shutting down to minimize the problem. Opening up the hood would also help but that's not always possible in public parking lot. Winter formulated gas between September and April has a lower boiling point than summer gas along with containing 10 percent alcohol, which exacerbates the problem year-round. Living in Central Florida doesn't help matters either. We all know how hot the Supra engine runs. I'm going to try a trick next time and jumper the B+ and Fp on the diagnostic block and let the fuel pump run for a minute to flush any vapor out of the rail before I try to start the engine. There is one station in town that sells old-fashioned pure gasoline at a premium price. I may try a few gallons of that if I can't find out what's going on. If that doesn’t work, I may have to swap out the igniter and /or the cam position sensor to rule those out.

[Bru]

The issues I was having with rough idling on starting a hot engine after sitting 20 or 30 minutes have basically gone away. I was thinking of replacing the cam position sensor when I thought maybe the problem is in the harness side. I noticed that the wires that went to the cam position sensor were looped down under some of the others in the harness where they branch apart as they come out of the plastic tunnel heat shield. Now that wire comes straight out on top and over to the cam positioned sensor plug. I no longer have to wiggle any wires or push on the rubber gromet that goes into the cam position sensor. I also had the P and Q letters connected backwards on the EGR vacuum modulator because I took off the cap to look inside at the filter and put it on backwards. The decal on top misled me. Those letters are also embossed on the base which are always correct. I've had some good experience with products made by Lubro Molly such as: Jectron Fuel Injection Cleaner ($5 at NAPA),Ventil Sauber Valve Cleaner ($4 at NAPA). The MoS2 Anti-Friction Engine Treatment makes the oil look dirty but it does run slightly cooler and makes the engine rev freer. I put half a can in the engine and the other half in the manual transmission where I am using 10W-30 motor oil anyway and a half a can of Lubro Moly "oil saver" to stop seal leaks. Shifts are improved. They make a concentrate specifically for gearboxes and rear ends (not for LSD though).
I got a tank of bad premium? gas and I improved it significantly by using a bottle of Lucas octane booster ($9 at Advance Auto on sale). They claim 3 to 4 octane numbers or 30 to 40 points on a tankful. Some boostaholics mix it with good premium gas for an added cushion to forestall knocking that retards the spark timing.

[Bru]

After my last posting, the problem with not starting when hot came back. It was like the timing was off the way it cranked. All I had to do was wiggle the wiring at the cam position sensor housing and it would start. Then it got worse by shutting down on the road while driving. Not good. I was also getting a code 14 for the Igniter but since wiring connects them I figured that the problem was in the wiring. This is what fixed it. There is a bundle of 3 ground wires that are crimped to a 4th wire that goes to the cam position sensor plug under the tape wrapping between the plug and the CPS housing. I unwrapped the wiring and cut the copper crimp open with a small pair of nippers. I guess a dremmel wheel would work also (wear safety glasses). I released the grip of the crimp by using a second pair of mini pliers. The wires looked a bit oxidized so I scraped them clean with a razor blade. They appear to be silver. I used radio shack lead free solder (tin/silver) and some flux to solder the 3 ground wires together and to the wire that goes to the plug. I wrapped and insulated the ground bundle before wrapping up the bundle against the other 3 positive wires insulation as it was before. After 2 weeks I have had no issues. Fuel mileage has actually increased by about 1 mpg or 5% to 20.2 mpg. This must be another Supra Achilles heel that takes years to appear.

Update:05-10-12 The problems came back. I got a got a cam position sensor that was only a few years in use. see my posting below.

[lmmr74]

Hi, i?m having the same hot starting issues. Can you please post some pics to illustrate what you did exactly, so that i can try the same?

Thanks in advance!

[Bru]

All the fixes I attemped with the wiring harness of the cam position sensor were only temporary in success. I finially got a cam position sensor that was only a few years in use.
That has solved all the issues with rough warm starting and the timing being occasionally off until the wiring is wiggled.