Bosch plugs cause hard starting?

Had a problem with our '00 Silverado 4x4 with 5.3 engine, over 110,000 miles. It would start fine when cold but when hot, it would crank over for more than 5 seconds before it would start, then stumble for a few seconds
before the idle was smooth. Gas mileage was not affected, and there was no black smoke when it did start, but I could smell gasoline. I replaced the fuel filter, installed new Bosch platinum plugs, new plug wires, cleaned K&N air filter, and cleaned out the air intake. The problem remained, and I didn't have the time to troubleshoot it, so my wife took it to the Chevy dealer. First, they replaced the O2 sensor, but that didn't fix it so we took it back. The next trip to the dealer they replaced the fuel regulator & the spark plugs with AC Delco brand. They claimed the hard starting was caused by the Bosch plugs not firing until the rpm's were up. I've been working on cars for 30 years and have never heard of this. Anyone else seen it? Thanks, Robert
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While Bosch Platinum plugs tend to be crap and cause lots of problems, your hard hot start problem was more than likely caused by a leaking fuel pressure regulator. Pretty common problem on the 5.3
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wrote:

On my ?? Jeep Cherokee the factory plugs gave me a very rough idle. The rough idle was solved by the Bosh Platinum plugs, no other changes were made. I took the truck in for an idle sensor setting and they did a full tune up. The rough idle came back. I immediately replaced them with the Bosh Platinum and again had a smooth idle.
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You don't know what year your Jeep is/was?

No such thing as an "idle sensor" on a Jeep.

Gee, I work on a lot of Jeeps and have never had a problem using what the OEM put in there originally. I also cure a lot of poor running engine by shit-canning Bosch Platinum plugs that are only a few weeks old... I can also guarantee you that a late model GM coil near plug ignition system will blast the Platinum coating off the tip of the electrode of those plugs in short order. Boschs' target market is unsuspecting DIYers.
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Well, I just learned something. I'll be sure to ask for the AC Delco iridium plugs the next time I'm in the parts store & need plugs. Thanks for the heads-up. Robert
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wrote:

Nope. Been too long. Possible '88 or '86. I didn't keep track of what year what vehicle was.

Idle position sensor.

Mine lasted for over 50,000 miles running smooth in the Jeep. In my current '98 Toyota Corolla has over 75,000 miles and is still running strong. The Suburban is still on the factory plugs (only about 40,000 on it) so no need to change.

See above.
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